llvm: Add llvm-config wrapper to improve flags handling

Add a wrapper for llvm-config which provides flags from the current envrionment
instead of the values hardcoded into llvm-native at compile time. Inspiration
taken from the wrapper in meta-clang but I had to totally rewrite it as:

* the TARGET_* prefixes weren't in our environment
* meson uses --libs --ldflags XXX which didn't work

(From OE-Core rev: 193ee1973f613b72f7f99660aecf652b07652d18)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-devtools/llvm/llvm_git.bb

@@ -31,6 +31,7 @@ SRC_URI = "git://github.com/llvm/llvm-project.git;branch=${BRANCH};protocol=http
            file://0006-llvm-TargetLibraryInfo-Undefine-libc-functions-if-th.patch;striplevel=2 \
            file://0007-llvm-allow-env-override-of-exe-path.patch;striplevel=2 \
            file://0001-AsmMatcherEmitter-sort-ClassInfo-lists-by-name-as-we.patch;striplevel=2 \
+           file://llvm-config \
            "
 
 UPSTREAM_CHECK_GITTAGREGEX = "llvmorg-(?P<pver>\d+(\.\d+)+)"
@@ -124,6 +125,15 @@ do_install() {
 do_install:class-native() {
 	install -D -m 0755 ${B}/bin/llvm-tblgen ${D}${bindir}/llvm-tblgen${PV}
 	install -D -m 0755 ${B}/bin/llvm-config ${D}${bindir}/llvm-config${PV}
+	ln -sf llvm-config${PV} ${D}${bindir}/llvm-config
+}
+
+SYSROOT_PREPROCESS_FUNCS:append:class-target = " llvm_sysroot_preprocess"
+
+llvm_sysroot_preprocess() {
+	install -d ${SYSROOT_DESTDIR}${bindir_crossscripts}/
+	install -m 0755 ${WORKDIR}/llvm-config ${SYSROOT_DESTDIR}${bindir_crossscripts}/
+	ln -sf llvm-config ${SYSROOT_DESTDIR}${bindir_crossscripts}/llvm-config${PV}
 }
 
 PACKAGES =+ "${PN}-bugpointpasses ${PN}-llvmhello ${PN}-libllvm ${PN}-liboptremarks ${PN}-liblto"