glibc: Always use GCC toolchain

Glibc is not yet buildable with non-gcc compilers e.g. clang

(From OE-Core rev: c822caf008be2311be3402a74826c6dcf99ce0a4)

Signed-off-by: Khem Raj <raj.khem@gmail.com>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-core/glibc/glibc-common.inc

@@ -23,3 +23,5 @@ ARM_INSTRUCTION_SET:armv6 = "arm"
 COMPATIBLE_HOST:libc-musl:class-target = "null"
 
 PV = "2.41+git"
+
+TOOLCHAIN = "gcc"