external-arm-toolchain: rebuild libmvec.so symlink if any

On some architectures (namely Aarch64), glibc may provide a libmvec
library since glibc 2.22, which programs built with gcc OpenMP
support might get linked to.

In order for these programs to work on the target, we need to copy this
library to the target filesystem.

Make sure that libmvec.so symlink is correct with or without usermerge
enabled otherwise libmvec.so symlink is broken.

For more details on libmvec, see
https://sourceware.org/glibc/wiki/libmvec.

(cherry picked from commit de47f836e282ad07bdaa72086a96c59e847b880b)

Signed-off-by: Romain Naour <romain.naour@smile.fr>
Acked-by: Denys Dmytriyenko <denys@konsulko.com>
Signed-off-by: Romain Naour <romain.naour@smile.fr>
Signed-off-by: Jon Mason <jon.mason@arm.com>

meta-arm-toolchain/recipes-devtools/external-arm-toolchain/external-arm-toolchain.bb

@@ -136,6 +136,9 @@ do_install() {
 		ln -sf ../../lib/libnss_compat.so.2 ${D}${libdir}/libnss_compat.so
 		ln -sf ../../lib/libm.so.6 ${D}${libdir}/libm.so
 		ln -sf ../../lib/libc_malloc_debug.so.0 ${D}${libdir}/libc_malloc_debug.so
+		if [ -f ${D}${base_libdir}/libmvec.so.1 ]; then
+			ln -sf ../../lib/libmvec.so.1 ${D}${libdir}/libmvec.so
+		fi
 
 		# remove potential .so duplicates from base_libdir
 		# for all symlinks created above in libdir
@@ -154,6 +157,7 @@ do_install() {
 		rm -f ${D}${base_libdir}/libnss_files.so
 		rm -f ${D}${base_libdir}/libnss_compat.so
 		rm -f ${D}${base_libdir}/libm.so
+		rm -f ${D}${base_libdir}/libmvec.so
 
 		# Move these completely to ${libdir} and delete duplicates in ${base_libdir}
 		for lib in asan hwasan atomic gfortran gomp itm lsan sanitizer stdc++ tsan ubsan; do
@@ -184,6 +188,9 @@ do_install() {
 		ln -sf libnss_compat.so.2 ${D}${libdir}/libnss_compat.so
 		ln -sf libm.so.6 ${D}${libdir}/libm.so
 		ln -sf libc_malloc_debug.so.0 ${D}${libdir}/libc_malloc_debug.so
+		if [ -f ${D}${libdir}/libmvec.so.1 ]; then
+			ln -sf libmvec.so.1 ${D}${libdir}/libmvec.so
+		fi
 	fi
 
 	# Besides ld-${EAT_VER_LIBC}.so, other libs can have duplicates like lib*-${EAT_VER_LIBC}.so