selftests/nolibc: don't use libgcc when building with clang

The logic in clang to find the libgcc.a from a GCC toolchain for a
specific ABI does not work reliably and can lead to errors.
Instead disable libgcc when building with clang, as it's not needed
anyways.
Acked-by: Willy Tarreau <w@1wt.eu>
Reviewed-by: Shuah Khan <skhan@linuxfoundation.org>
Link: https://lore.kernel.org/r/20240807-nolibc-llvm-v2-13-c20f2f5fc7c2@weissschuh.netSigned-off-by: Thomas Weißschuh <linux@weissschuh.net>

tools/testing/selftests/nolibc/Makefile

@@ -157,6 +157,13 @@ CFLAGS  ?= -Os -fno-ident -fno-asynchronous-unwind-tables -std=c89 -W -Wall -Wex
 		$(CFLAGS_$(XARCH)) $(CFLAGS_STACKPROTECTOR) $(CFLAGS_EXTRA)
 LDFLAGS :=
 
+LIBGCC := -lgcc
+
+ifneq ($(LLVM),)
+# Not needed for clang
+LIBGCC :=
+endif
+
 # Modify CFLAGS based on LLVM=
 include $(srctree)/tools/scripts/Makefile.include
 
@@ -209,11 +216,11 @@ sysroot/$(ARCH)/include:
 ifneq ($(NOLIBC_SYSROOT),0)
 nolibc-test: nolibc-test.c nolibc-test-linkage.c sysroot/$(ARCH)/include
 	$(QUIET_CC)$(CC) $(CFLAGS) $(LDFLAGS) -o $@ \
-	  -nostdlib -nostdinc -static -Isysroot/$(ARCH)/include nolibc-test.c nolibc-test-linkage.c -lgcc
+	  -nostdlib -nostdinc -static -Isysroot/$(ARCH)/include nolibc-test.c nolibc-test-linkage.c $(LIBGCC)
 else
 nolibc-test: nolibc-test.c nolibc-test-linkage.c
 	$(QUIET_CC)$(CC) $(CFLAGS) $(LDFLAGS) -o $@ \
-	  -nostdlib -static -include $(srctree)/tools/include/nolibc/nolibc.h nolibc-test.c nolibc-test-linkage.c -lgcc
+	  -nostdlib -static -include $(srctree)/tools/include/nolibc/nolibc.h nolibc-test.c nolibc-test-linkage.c $(LIBGCC)
 endif
 
 libc-test: nolibc-test.c nolibc-test-linkage.c