CMake: Fix detection of linker availability

Previously we passed flags like -ld-fuse=lld only to compile
calls, but not to the link call of a compile test project.

Make sure to pass it to the link call instead by using
check_cxx_source_compiles + CMAKE_REQUIRED_LINK_OPTIONS
instead of
check_cxx_compiler_flag.

Note the flag that is passed is still via passed via the
compiler launcher and not directly to the linker.

Remove duplicate flag handling code.

Change-Id: I1bf90573904a9df83240b6debfee3cc9e425c6bb
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Joerg Bornemann <joerg.bornemann@qt.io>
(cherry picked from commit d6066d53fa70e1736ca64d468605a4a430644400)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

3 files changed, 36 insertions, 16 deletions

diff --git a/cmake/QtFeature.cmake b/cmake/QtFeature.cmake
index 09a1c8361c..3ade942f17 100644
--- a/cmake/QtFeature.cmake
+++ b/cmake/QtFeature.cmake
@@ -1118,6 +1118,33 @@ function(qt_config_compiler_supports_flag_test name)
     set(TEST_${name} "${TEST_${name}}" CACHE INTERNAL "${label}")
 endfunction()
 
+function(qt_internal_get_active_linker_flags out_var)
+    set(flags "")
+    if(GCC OR CLANG)
+        if(QT_FEATURE_use_gold_linker)
+            list(APPEND flags "-fuse-ld=gold")
+        elseif(QT_FEATURE_use_bfd_linker)
+            list(APPEND flags "-fuse-ld=bfd")
+        elseif(QT_FEATURE_use_lld_linker)
+            list(APPEND flags "-fuse-ld=lld")
+        endif()
+    endif()
+    set(${out_var} "${flags}" PARENT_SCOPE)
+endfunction()
+
+function(qt_internal_check_if_linker_is_available name)
+    if(DEFINED "TEST_${name}")
+        return()
+    endif()
+
+    cmake_parse_arguments(arg "" "LABEL;FLAG" "" ${ARGN})
+    set(flags "${arg_FLAG}")
+
+    set(CMAKE_REQUIRED_LINK_OPTIONS ${flags})
+    check_cxx_source_compiles("int main() { return 0; }" TEST_${name})
+    set(TEST_${name} "${TEST_${name}}" CACHE INTERNAL "${label}")
+endfunction()
+
 function(qt_config_linker_supports_flag_test name)
     if(DEFINED "TEST_${name}")
         return()
@@ -1126,15 +1153,10 @@ function(qt_config_linker_supports_flag_test name)
     cmake_parse_arguments(arg "" "LABEL;FLAG" "" ${ARGN})
     set(flags "-Wl,${arg_FLAG}")
 
-    # Select the right linker.
-    if(GCC OR CLANG)
-        if(QT_FEATURE_use_gold_linker)
-            list(PREPEND flags "-fuse-ld=gold")
-        elseif(QT_FEATURE_use_bfd_linker)
-            list(PREPEND flags "-fuse-ld=bfd")
-        elseif(QT_FEATURE_use_lld_linker)
-            list(PREPEND flags "-fuse-ld=lld")
-        endif()
+    # Pass the linker that the main project uses to the compile test.
+    qt_internal_get_active_linker_flags(linker_flags)
+    if(linker_flags)
+        list(PREPEND flags ${linker_flags})
     endif()
 
     set(CMAKE_REQUIRED_LINK_OPTIONS ${flags})
diff --git a/cmake/QtInternalTargets.cmake b/cmake/QtInternalTargets.cmake
index d8fa48f236..aef0c76abf 100644
--- a/cmake/QtInternalTargets.cmake
+++ b/cmake/QtInternalTargets.cmake
@@ -248,13 +248,11 @@ if(DEFINED QT_EXTRA_FRAMEWORKPATHS AND APPLE)
     unset(__qt_fw_flags)
 endif()
 
-if(QT_FEATURE_use_gold_linker)
-    target_link_options(PlatformCommonInternal INTERFACE "-fuse-ld=gold")
-elseif(QT_FEATURE_use_bfd_linker)
-    target_link_options(PlatformCommonInternal INTERFACE "-fuse-ld=bfd")
-elseif(QT_FEATURE_use_lld_linker)
-    target_link_options(PlatformCommonInternal INTERFACE "-fuse-ld=lld")
+qt_internal_get_active_linker_flags(__qt_internal_active_linker_flags)
+if(__qt_internal_active_linker_flags)
+    target_link_options(PlatformCommonInternal INTERFACE "${__qt_internal_active_linker_flags}")
 endif()
+unset(__qt_internal_active_linker_flags)
 
 if(QT_FEATURE_enable_gdb_index)
     target_link_options(PlatformCommonInternal INTERFACE "-Wl,--gdb-index")
diff --git a/cmake/QtProcessConfigureArgs.cmake b/cmake/QtProcessConfigureArgs.cmake
index 6342df93bd..2440f63627 100644
--- a/cmake/QtProcessConfigureArgs.cmake
+++ b/cmake/QtProcessConfigureArgs.cmake
@@ -151,7 +151,7 @@ defstub(qt_find_package)
 defstub(set_package_properties)
 defstub(qt_qml_find_python)
 defstub(qt_set01)
-
+defstub(qt_internal_check_if_linker_is_available)
 
 ####################################################################################################
 # Define functions/macros that are called in qt_cmdline.cmake files