CMake: Fix usage of gc_binaries feature

The qt_internal_apply_gc_binaries function should apply both compile
and link flags, not just link flags.

The flags should be applied publically to all consumers of Bootstrap
regardless if the gc_binaries feature is enabled.

The flags should be applied publically to Core only in case if the
feature is enabled (aka for static builds only).

Change-Id: Id42af0d9b527004d74c04eff2c9e3c2be1e76aac
Fixes: QTBUG-84461
Task-number: QTBUG-83929
Reviewed-by: Cristian Adam <cristian.adam@qt.io>

cmake/QtBuild.cmake

@@ -1409,7 +1409,15 @@ function(qt_internal_add_link_flags_no_undefined target)
     endif()
 endfunction()
 
-function(qt_internal_add_link_flags_gc_sections target visibility)
+function(qt_internal_apply_gc_binaries_conditional target visibility)
+    # Should only be applied when the feature is enabled, aka for static builds.
+    if(NOT QT_FEATURE_gc_binaries)
+        return()
+    endif()
+    qt_internal_apply_gc_binaries("${target}" "${visibility}")
+endfunction()
+
+function(qt_internal_apply_gc_binaries target visibility)
     set(possible_visibilities PRIVATE INTERFACE PUBLIC)
     list(FIND possible_visibilities "${visibility}" known_visibility)
     if (known_visibility EQUAL "-1")
@@ -1419,13 +1427,22 @@ function(qt_internal_add_link_flags_gc_sections target visibility)
     if ((GCC OR CLANG) AND NOT EMSCRIPTEN)
         if(APPLE)
             set(gc_sections_flag "-Wl,-dead_strip")
-        elseif(LINUX OR BSD OR SOLARIS OR WIN32 OR ANDROID)
+        elseif(SOLARIS)
+            set(gc_sections_flag "-Wl,-z,ignore")
+        elseif(LINUX OR BSD OR WIN32 OR ANDROID)
             set(gc_sections_flag "-Wl,--gc-sections")
-        else()
-            message(FATAL_ERROR "Platform linker doesn't support gc sections. Target:\"${target}\".")
         endif()
+    endif()
+    if(gc_sections_flag)
         target_link_options("${target}" ${visibility} "${gc_sections_flag}")
     endif()
+
+    if((GCC OR CLANG OR ICC) AND NOT EMSCRIPTEN)
+        set(split_sections_flags "-ffunction-sections" "-fdata-sections")
+    endif()
+    if(split_sections_flags)
+        target_compile_options("${target}" ${visibility} ${split_sections_flags})
+    endif()
 endfunction()
 
 function(qt_internal_add_linker_version_script target)

configure.cmake

@@ -355,6 +355,9 @@ qt_feature("cross_compile" PUBLIC
 )
 qt_feature_config("cross_compile" QMAKE_PUBLIC_CONFIG)
 qt_feature_config("cross_compile" QMAKE_PRIVATE_CONFIG)
+qt_feature("gc_binaries" PRIVATE
+    CONDITION NOT QT_FEATURE_shared
+)
 qt_feature("use_bfd_linker"
     LABEL "bfd"
     AUTODETECT false

qmake/CMakeLists.txt

@@ -270,7 +270,7 @@ set_target_properties(${target_name} PROPERTIES
     AUTOUIC OFF
 )
 
-qt_internal_add_link_flags_gc_sections(${target_name} PRIVATE) # special case
+qt_internal_apply_gc_binaries(${target_name} PRIVATE) # special case
 
 qt_enable_msvc_cplusplus_define(${target_name} PUBLIC) # special case
 qt_skip_warnings_are_errors(${target_name}) # special case

src/corelib/CMakeLists.txt

@@ -1272,7 +1272,7 @@ if(WIN32)
     set_target_properties(Core PROPERTIES COMPILE_DEFINITIONS "${defines}")
 endif()
 
-qt_internal_add_link_flags_gc_sections(Core PRIVATE)
+qt_internal_apply_gc_binaries_conditional(Core PUBLIC)
 
 if(WIN32)
     set(isExe $<STREQUAL:$<TARGET_PROPERTY:TYPE>,EXECUTABLE>)

src/tools/bootstrap/CMakeLists.txt

@@ -261,7 +261,7 @@ qt_extend_target(Bootstrap CONDITION MINGW AND WIN32
 # QMAKE_CFLAGS = "$$QMAKE_CFLAGS_SHSTK"
 
 # special case begin
-qt_internal_add_link_flags_gc_sections(Bootstrap PUBLIC)
+qt_internal_apply_gc_binaries(Bootstrap PUBLIC)
 set_target_properties(Bootstrap PROPERTIES AUTOMOC OFF AUTOUIC OFF AUTORCC OFF)
 qt_internal_add_target_aliases(Bootstrap)
 qt_enable_msvc_cplusplus_define(Bootstrap PUBLIC)

util/cmake/configurejson2cmake.py

@@ -863,7 +863,9 @@ def get_feature_mapping():
         "framework": {
             "condition": "APPLE AND BUILD_SHARED_LIBS AND NOT CMAKE_BUILD_TYPE STREQUAL Debug"
         },
-        "gc_binaries": None,
+        "gc_binaries": {
+            "condition" : "NOT QT_FEATURE_shared"
+        },
         "gcc-sysroot": None,
         "gcov": None,
         "gnu-libiconv": {