Index: uspace/lib/c/arch/amd64/Makefile.common
===================================================================
--- uspace/lib/c/arch/amd64/Makefile.common	(revision 5b0cf635022b821f28f7a014ad5b39d005cd7666)
+++ uspace/lib/c/arch/amd64/Makefile.common	(revision fec0240ef06fc1a62210bc1e0e106291c3ed64fb)
@@ -31,5 +31,8 @@
 # XXX: clang doesn't support this flag, but the optimization is OS-specific,
 #      so it isn't used for amd64-unknown-elf target.
-GCC_CFLAGS += -mno-tls-direct-seg-refs
+
+ifneq ($(COMPILER),clang)
+	COMMON_CFLAGS += -mno-tls-direct-seg-refs
+endif
 
 LFLAGS += --gc-sections