toolchain/gcc: fix build on arm with clang as host gcc replacement

Signed-off-by: Felix Fietkau <nbd@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@40772 3c298f89-4303-0410-b956-a3cf2f4a3e73

toolchain/gcc/common.mk

@@ -95,6 +95,10 @@ endif
 
 GCC_CONFIGURE:= \
 	SHELL="$(BASH)" \
+	$(if $(shell gcc --version 2>&1 | grep LLVM), \
+		CFLAGS="-O2 -fbracket-depth=512 -pipe" \
+		CXXFLAGS="-O2 -fbracket-depth=512 -pipe" \
+	) \
 	$(HOST_SOURCE_DIR)/configure \
 		--with-bugurl=$(BUGURL) \
 		--with-pkgversion="$(PKGVERSION)" \