target-gcc: fix build

Now that $(STAGING_DIR)/usr/bin is no longer in the PATH, we need to
pass the absolute paths to $(TARGET_CC) when building the target gcc
compiler.

This commit fixes the target gcc build problem reported on the list. I
have successfully been able to build a target gcc for ARM, use it to
compile a hello world application on the target and run this
application.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

toolchain/gcc/gcc-uclibc-4.x.mk

@@ -397,6 +397,8 @@ $(GCC_BUILD_DIR3)/.configured: $(GCC_BUILD_DIR3)/.prepared
 		CXXFLAGS_FOR_TARGET="$(TARGET_CFLAGS) $(TARGET_SOFT_FLOAT)" \
 		CFLAGS="$(TARGET_CFLAGS) $(TARGET_SOFT_FLOAT)" \
 		BOOT_CFLAGS="$(TARGET_CFLAGS) $(TARGET_SOFT_FLOAT)" \
+		GCC_FOR_TARGET="$(TARGET_CC)" \
+		CC_FOR_TARGET="$(TARGET_CC)" \
 		$(GCC_SRC_DIR)/configure $(QUIET) \
 		--prefix=/usr \
 		--build=$(GNU_HOST_NAME) \