Use CFLAGS when linking.  Some flags can add functionality to generated
code that requires extra libs to be linked in (eg. libgomp when using
autoparallelization).  Other flags are required when building and linking
(eg. -flto).

https://bugs.gentoo.org/365975

--- a/config/autoconf.mk.in
+++ b/config/autoconf.mk.in
@@ -81,6 +81,7 @@ OS_DLLFLAGS	= @OS_DLLFLAGS@
 DLLFLAGS	= @DLLFLAGS@
 EXEFLAGS  = @EXEFLAGS@
 OPTIMIZER	= @OPTIMIZER@
+LD_CFLAGS   = @CFLAGS@
 
 PROFILE_GEN_CFLAGS  = @PROFILE_GEN_CFLAGS@
 PROFILE_GEN_LDFLAGS = @PROFILE_GEN_LDFLAGS@
--- a/config/config.mk
+++ b/config/config.mk
@@ -72,7 +72,7 @@ NOMD_CFLAGS	= $(CC_ONLY_FLAGS) $(OPTIMIZER) $(NOMD_OS_CFLAGS)\
 NOMD_CCFLAGS	= $(CCC_ONLY_FLAGS) $(OPTIMIZER) $(NOMD_OS_CFLAGS)\
 		  $(XP_DEFINE) $(DEFINES) $(INCLUDES) $(XCFLAGS)
 
-LDFLAGS		= $(OS_LDFLAGS)
+LDFLAGS		= $(LD_CFLAGS) $(OS_LDFLAGS)
 
 # Enable profile-guided optimization
 ifdef MOZ_PROFILE_GENERATE