meta: Add TCOVERRIDE for toolchain selection at recipe scope

TCOVERRIDE is defined to toolchain-<TOOLCHAIN> and its added to OVERRIDES
that a recipe can see and it can use "toolchain-gcc" or "toolchain-clang"
to set specific metadata based upon global distro toolchain policy.

(From OE-Core rev: 6010f47124d9067609bbe5d9ff16193c8bf79acf)

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/conf/bitbake.conf

@@ -801,7 +801,7 @@ DISTRO_NAME ??= "OpenEmbedded"
 # And finally '<foo>:forcevariable' overrides any standard variable, with the highest priority.
 # This works for functions as well, they are really just variables.
 #
-OVERRIDES = "${TARGET_OS}:${TRANSLATED_TARGET_ARCH}:pn-${PN}:layer-${FILE_LAYERNAME}:${MACHINEOVERRIDES}:${DISTROOVERRIDES}:${CLASSOVERRIDE}${LIBCOVERRIDE}:forcevariable"
+OVERRIDES = "${TARGET_OS}:${TRANSLATED_TARGET_ARCH}:pn-${PN}:layer-${FILE_LAYERNAME}:${MACHINEOVERRIDES}:${DISTROOVERRIDES}:${CLASSOVERRIDE}:${TCOVERRIDE}${LIBCOVERRIDE}:forcevariable"
 FILE_LAYERNAME ??= "config"
 LIBCOVERRIDE ?= ""
 CLASSOVERRIDE ?= "class-target"

meta/conf/toolchain/clang.inc

@@ -30,3 +30,5 @@ TUNE_CCARGS += "${@bb.utils.contains("DISTRO_FEATURES", "usrmerge", " --dyld-pre
 
 LDFLAGS:append:class-nativesdk:x86-64 = " -Wl,-dynamic-linker,${base_libdir}/ld-linux-x86-64.so.2"
 LDFLAGS:append:class-nativesdk:aarch64 = " -Wl,-dynamic-linker,${base_libdir}/ld-linux-aarch64.so.1"
+
+TCOVERRIDE = "toolchain-clang"

meta/conf/toolchain/gcc.inc

@@ -24,3 +24,4 @@ PREFERRED_PROVIDER_virtual/nativesdk-cross-cc = "gcc-crosssdk-${SDK_SYS}"
 PREFERRED_PROVIDER_virtual/nativesdk-cross-c++ = "gcc-crosssdk-${SDK_SYS}"
 PREFERRED_PROVIDER_virtual/nativesdk-compilerlibs = "nativesdk-gcc-runtime"
 
+TCOVERRIDE = "toolchain-gcc"