Revert "Detect C standard and try using the most recent"

The change causes a crash when compiling the xkbcommon 3rdparty
library and compile failures (qtimageformats on Android).

This reverts commit a47cb146809e32f43449dcfe9932833c2f0ab987.

Task-number: QTBUG-67326
Task-number: QTBUG-67327
Change-Id: I5ddc4eccad699e3eaec535fd6a63d11b0026b42e
Reviewed-by: Sami Nurmenniemi <sami.nurmenniemi@qt.io>
Reviewed-by: Liang Qi <liang.qi@qt.io>
Reviewed-by: Gatis Paeglis <gatis.paeglis@qt.io>

configure.json

@@ -259,36 +259,6 @@
             "type": "compile",
             "test": "stl"
         },
-        "c99": {
-            "label": "C99 support",
-            "type": "compile",
-            "test": {
-                "head": [
-                    "#if __STDC_VERSION__ >= 199901L",
-                    "// Compiler claims to support C99, trust it",
-                    "#else",
-                    "#  error __STDC_VERSION__ must be >= 199901L",
-                    "#endif"
-                ],
-                "lang": "c",
-                "qmake": "CONFIG += c99"
-            }
-        },
-        "c11": {
-            "label": "C11 support",
-            "type": "compile",
-            "test": {
-                "head": [
-                    "#if __STDC_VERSION__ >= 201112L",
-                    "// Compiler claims to support C11, trust it",
-                    "#else",
-                    "#  error __STDC_VERSION__ must be >= 201112L",
-                    "#endif"
-                ],
-                "lang": "c",
-                "qmake": "CONFIG += c11"
-            }
-        },
         "c++14": {
             "label": "C++14 support",
             "type": "compile",
@@ -816,19 +786,6 @@
             "condition": "features.c++14 && tests.c++1z",
             "output": [ "publicFeature", "publicQtConfig" ]
         },
-        "c89": {
-            "label": "C89"
-        },
-        "c99": {
-            "label": "C99",
-            "condition": "tests.c99",
-            "output": [ "publicFeature" ]
-        },
-        "c11": {
-            "label": "C11",
-            "condition": "features.c99 && tests.c11",
-            "output": [ "publicFeature" ]
-        },
         "precompile_header": {
             "label": "Using precompiled headers",
             "condition": "config.msvc || tests.precompile_header",
@@ -1289,11 +1246,6 @@ Configure with '-qreal float' to create a build that is binary-compatible with 5
                     "condition": "!features.debug || features.debug_and_release"
                 },
                 "shared",
-                {
-                    "message": "Using C standard",
-                    "type": "firstAvailableFeature",
-                    "args": "c11 c99 c89"
-                },
                 {
                     "message": "Using C++ standard",
                     "type": "firstAvailableFeature",

mkspecs/common/android-base-tail.conf

@@ -38,8 +38,6 @@ QMAKE_CFLAGS_THREAD     = -D_REENTRANT
 QMAKE_CFLAGS_HIDESYMS   = -fvisibility=hidden
 QMAKE_CFLAGS_NEON       = -mfpu=neon
 
-QMAKE_CFLAGS_GNUC99     = -std=gnu99
-QMAKE_CFLAGS_GNUC11     = -std=gnu11
 QMAKE_CXXFLAGS_CXX11    = -std=c++11
 QMAKE_CXXFLAGS_CXX14    = -std=c++14
 QMAKE_CXXFLAGS_CXX1Z    = -std=c++1z

mkspecs/common/clang.conf

@@ -21,8 +21,6 @@ QMAKE_CFLAGS_PRECOMPILE          = -x c-header -c ${QMAKE_PCH_INPUT} -o ${QMAKE_
 QMAKE_CFLAGS_USE_PRECOMPILE      = -Xclang -include-pch -Xclang ${QMAKE_PCH_OUTPUT}
 QMAKE_CFLAGS_LTCG                = -flto
 QMAKE_CFLAGS_DISABLE_LTCG        = -fno-lto
-QMAKE_CFLAGS_GNUC99              = -std=gnu99
-QMAKE_CFLAGS_GNUC11              = -std=gnu11
 
 QMAKE_CXXFLAGS_PRECOMPILE        = -x c++-header -c ${QMAKE_PCH_INPUT} -o ${QMAKE_PCH_OUTPUT}
 QMAKE_CXXFLAGS_USE_PRECOMPILE    = $$QMAKE_CFLAGS_USE_PRECOMPILE

mkspecs/common/g++-base.conf

@@ -27,8 +27,6 @@ QMAKE_CFLAGS_USE_PRECOMPILE   = -include ${QMAKE_PCH_OUTPUT_BASE}
 QMAKE_CXXFLAGS_PRECOMPILE     = -x c++-header -c ${QMAKE_PCH_INPUT} -o ${QMAKE_PCH_OUTPUT}
 QMAKE_CXXFLAGS_USE_PRECOMPILE = $$QMAKE_CFLAGS_USE_PRECOMPILE
 
-QMAKE_CFLAGS_GNUC99     = -std=gnu99
-QMAKE_CFLAGS_GNUC11     = -std=gnu11
 QMAKE_CXXFLAGS_CXX11    = -std=c++11
 QMAKE_CXXFLAGS_CXX14    = -std=c++1y
 QMAKE_CXXFLAGS_CXX1Z    = -std=c++1z

mkspecs/common/gcc-base.conf

@@ -81,9 +81,6 @@ QMAKE_LFLAGS_RELEASE_WITH_DEBUGINFO +=
 QMAKE_LFLAGS_EXCEPTIONS_OFF +=
 QMAKE_LFLAGS_LTCG       = $$QMAKE_CFLAGS_LTCG -fuse-linker-plugin
 
-QMAKE_CFLAGS_C99       = -std=c99
-QMAKE_CFLAGS_C11       = -std=c11
-
 QMAKE_CFLAGS_SSE2      += -msse2
 QMAKE_CFLAGS_SSE3      += -msse3
 QMAKE_CFLAGS_SSSE3     += -mssse3

mkspecs/features/default_post.prf

@@ -143,21 +143,6 @@ c++11|c++14|c++1z {
     unset(cxxstd)
 }
 
-c99|c11 {
-    c11:       cstd = C11
-    else:      cstd = C99
-
-    # Check if we should disable compiler extensions or not
-    !isEmpty(QMAKE_CFLAGS_GNU$$cstd) {
-        # Let strict C++ imply strict C
-        !strict_c++: cstd = GNU$$cstd
-    }
-
-    QMAKE_CFLAGS += $$eval(QMAKE_CFLAGS_$$cstd)
-
-    unset(cstd)
-}
-
 utf8_source {
     QMAKE_CFLAGS += $$QMAKE_CFLAGS_UTF8_SOURCE
     QMAKE_CXXFLAGS += $$QMAKE_CFLAGS_UTF8_SOURCE

mkspecs/features/qt_common.prf

@@ -17,8 +17,6 @@ DEFINES *= QT_NO_NARROWING_CONVERSIONS_IN_CONNECT
 qtConfig(c++11): CONFIG += c++11 strict_c++
 qtConfig(c++14): CONFIG += c++14
 qtConfig(c++1z): CONFIG += c++1z
-qtConfig(c99): CONFIG += c99
-qtConfig(c11): CONFIG += c11
 qtConfig(stack-protector-strong): CONFIG += stack_protector_strong
 contains(TEMPLATE, .*lib) {
     # module and plugins

mkspecs/features/qt_configure.prf

@@ -866,15 +866,6 @@ defineTest(qtConfTestPrepare_compile) {
 defineTest(qtConfPrepareCompileTestSource) {
     test_dir = $$2
 
-    test_lang = $$eval($${1}.lang)
-    isEmpty(test_lang): test_lang = "c++"
-
-    equals(test_lang, "c++"): suffix = "cpp"
-    else: equals(test_lang, "c"): suffix = "c"
-    else: equals(test_lang, "objc"): suffix = "m"
-    else: equals(test_lang, "objc++"): suffix = "mm"
-    else: error("Unknown language '$$test_lang' in compile test $$1")
-
     # Create source code
     contents = "/* Generated by configure */"
     # Custom code before includes
@@ -898,10 +889,10 @@ defineTest(qtConfPrepareCompileTestSource) {
         "    /* END TEST */" \
         "    return 0;" \
         "}"
-    write_file($$test_dir/main.$$suffix, contents)|error()
+    write_file($$test_dir/main.cpp, contents)|error()
 
     # Create stub .pro file
-    contents = "SOURCES = main.$$suffix"
+    contents = "SOURCES = main.cpp"
     # Custom project code
     for (ent, $$qtConfScalarOrList($${1}.qmake)): \
         contents += $$ent

src/3rdparty/xkbcommon.pri

@@ -1,3 +1,4 @@
+QMAKE_CFLAGS += -std=gnu99 -w
 INCLUDEPATH += $$PWD/xkbcommon \
                $$PWD/xkbcommon/xkbcommon \
                $$PWD/xkbcommon/src \

src/corelib/global/qcompilerdetection.h

@@ -898,7 +898,7 @@
        /* C11 features supported in GCC 4.7: */
 #      define Q_COMPILER_STATIC_ASSERT
 #    endif
-#    if Q_CC_GNU >= 409 && defined(__has_include)
+#    if Q_CC_GNU >= 409
        /* C11 features supported in GCC 4.9: */
 #      if __has_include(<threads.h>)
 #        define Q_COMPILER_THREAD_LOCAL