use -Wl,-dead_strip on Mac, its linker doesn't know -Wl,--gc-sections

Change-Id: Ic69d0030a46fe4753cc75da58bb2c15cf009b135
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/87023
Tested-by: Jenkins
Reviewed-by: Luboš Luňák <l.lunak@collabora.com>

config_host.mk.in

@@ -318,6 +318,7 @@ export KF5_LIBS=$(gb_SPACE)@KF5_LIBS@
 export KRB5_LIBS=@KRB5_LIBS@
 export LCMS2_CFLAGS=$(gb_SPACE)@LCMS2_CFLAGS@
 export LCMS2_LIBS=$(gb_SPACE)@LCMS2_LIBS@
+export LD_GC_SECTIONS=@LD_GC_SECTIONS@
 export LD_PLUGIN=@LD_PLUGIN@
 @x_LDFLAGS@ export LDFLAGS=@LDFLAGS@
 export LFS_CFLAGS=@LFS_CFLAGS@

configure.ac

@@ -4062,6 +4062,29 @@ printf ("hello world\n");
 fi
 AC_SUBST(HAVE_LD_BSYMBOLIC_FUNCTIONS)
 
+LD_GC_SECTIONS=
+if test "$GCC" = "yes"; then
+    for flag in "--gc-sections" "-dead_strip"; do
+        AC_MSG_CHECKING([for $flag linker support])
+        ldflags_save=$LDFLAGS
+        LDFLAGS="$LDFLAGS -Wl,$flag"
+        AC_LINK_IFELSE([AC_LANG_PROGRAM([
+#include <stdio.h>
+            ],[
+printf ("hello world\n");
+            ])],[
+            LD_GC_SECTIONS="-Wl,$flag"
+            AC_MSG_RESULT( found )
+            ], [
+            AC_MSG_RESULT( not found )
+            ])
+        LDFLAGS=$ldflags_save
+        if test -n "$LD_GC_SECTIONS"; then
+            break
+        fi
+    done
+fi
+AC_SUBST(LD_GC_SECTIONS)
 
 HAVE_GSPLIT_DWARF=
 if test "$enable_split_debug" != no; then

solenv/gbuild/platform/com_GCC_class.mk

@@ -95,7 +95,7 @@ gb_PrecompiledHeader_pch_with_obj = $(BUILDING_PCH_WITH_OBJ)
 ifneq ($(BUILDING_PCH_WITH_OBJ),)
 # If using Clang's PCH extra object, we may need to strip unused sections, otherwise inline and template functions
 # emitted in that object may in some cases cause unresolved references to private symbols in other libraries.
-gb_LinkTarget_LDFLAGS += -Wl,--gc-sections
+gb_LinkTarget_LDFLAGS += $(LD_GC_SECTIONS)
 gb_PrecompiledHeader_pch_with_obj += -ffunction-sections -fdata-sections
 # Enable generating more shared code and debuginfo in the PCH object file.
 gb_PrecompiledHeader_pch_with_obj += $(PCH_MODULES_DEBUGINFO)