pass --disable-bootstrap to gcc

this should be a nop since we're either building a cross compiler or
cross compiling, but due to recent gcc's config.guess detecting musl,
it's possible to spuriously get $build=$host=$target, and then the
dreaded bootstrap procedure runs and breaks the output.

litecross/Makefile

@@ -68,6 +68,7 @@ FULL_BINUTILS_CONFIG = \
 FULL_GCC_CONFIG = --enable-languages=c,c++ \
 	$(GCC_CONFIG_FOR_TARGET) \
 	$(COMMON_CONFIG) $(GCC_CONFIG) $(TOOLCHAIN_CONFIG) \
+	--disable-bootstrap \
 	--disable-werror \
 	--target=$(TARGET) --prefix= \
 	--libdir=/lib --disable-multilib \