rework detection and use of clock_gettime()/librt

recent versions of glibc include clock_gettime() inside libc itself.

Task-number: QTBUG-41009
Change-Id: I7401773be99682a356bf06a69571d11c4b15978b
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

config.tests/unix/clock-gettime/clock-gettime.pri

@@ -1,2 +0,0 @@
-# clock_gettime() is implemented in librt on these systems
-linux-*|hpux-*|solaris-*:LIBS_PRIVATE *= -lrt

config.tests/unix/clock-gettime/clock-gettime.pro

@@ -1,3 +1,2 @@
 SOURCES = clock-gettime.cpp
 CONFIG -= qt dylib
-include(clock-gettime.pri)

config.tests/unix/clock-monotonic/clock-monotonic.pro

@@ -1,3 +1,2 @@
 SOURCES = clock-monotonic.cpp
 CONFIG -= qt dylib
-include(../clock-gettime/clock-gettime.pri)

src/corelib/configure.json

@@ -84,6 +84,14 @@
                 "-ldl"
             ]
         },
+        "librt": {
+            "label": "clock_gettime()",
+            "test": "unix/clock-gettime",
+            "sources": [
+                "",
+                "-lrt"
+            ]
+        },
         "pcre2": {
             "label": "PCRE2",
             "test": "unix/pcre2",
@@ -119,15 +127,11 @@
             "type": "compile",
             "test": "common/atomicfptr"
         },
-        "clock-gettime": {
-            "label": "clock_gettime()",
-            "type": "compile",
-            "test": "unix/clock-gettime"
-        },
         "clock-monotonic": {
             "label": "POSIX monotonic clock",
             "type": "compile",
-            "test": "unix/clock-monotonic"
+            "test": "unix/clock-monotonic",
+            "use": "librt"
         },
         "cloexec": {
             "label": "O_CLOEXEC",
@@ -199,7 +203,7 @@
     "features": {
         "clock-gettime": {
             "label": "clock_gettime()",
-            "condition": "tests.clock-gettime",
+            "condition": "config.unix && libs.librt",
             "output": [ "privateFeature" ]
         },
         "clock-monotonic": {

src/corelib/kernel/kernel.pri

@@ -162,7 +162,7 @@ unix|integrity {
         QMAKE_USE_PRIVATE += glib
     }
 
-   qtConfig(clock-gettime): include($$QT_SOURCE_TREE/config.tests/unix/clock-gettime/clock-gettime.pri)
+    qtConfig(clock-gettime): QMAKE_USE_PRIVATE += librt
 
     !android {
         SOURCES += kernel/qsharedmemory_posix.cpp \