external-arm-toolchain: wrap base_libdir vs libdir manipulations under usrmerge check

With `usrmerge` disto feature `base_libdir` and `libdir` are the same,
so it does not make sense to:

* removing "duplicates" between them
* move files from `base_libdir` to `libdir`

This fixes build error

| mv: '.../tmp/work/cortexa15t2hf-neon-poky-linux-gnueabi/external-arm-toolchain/12.2.Rel1/image/usr/lib/libasan.a' and '.../tmp/work/cortexa15t2hf-neon-poky-linux-gnueabi/external-arm-toolchain/12.2.Rel1/image/usr/lib/libasan.a' are the same file

in case of `usrmerge` feature enabled.

(cherry picked from commit 98eea6296290b5aead0e8d9281a91fbd94c3bf4e)

Signed-off-by: Vasyl Vavrychuk <vvavrychuk@gmail.com>
Acked-by: Denys Dmytriyenko <denys@konsulko.com>
Signed-off-by: Romain Naour <romain.naour@smile.fr>
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

@@ -135,37 +135,39 @@ do_install() {
 	ln -sf ../../lib/libm.so.6 ${D}${libdir}/libm.so
 	ln -sf ../../lib/libc_malloc_debug.so.0 ${D}${libdir}/libc_malloc_debug.so
 
-	# remove potential .so duplicates from base_libdir
-	# for all symlinks created above in libdir
-	rm -f ${D}${base_libdir}/librt.so
-	rm -f ${D}${base_libdir}/libcrypt.so
-	rm -f ${D}${base_libdir}/libresolv.so
-	rm -f ${D}${base_libdir}/libnss_hesiod.so
-	rm -f ${D}${base_libdir}/libutil.so
-	rm -f ${D}${base_libdir}/libBrokenLocale.so
-	rm -f ${D}${base_libdir}/libpthread.so
-	rm -f ${D}${base_libdir}/libthread_db.so
-	rm -f ${D}${base_libdir}/libanl.so
-	rm -f ${D}${base_libdir}/libdl.so
-	rm -f ${D}${base_libdir}/libnss_db.so
-	rm -f ${D}${base_libdir}/libnss_dns.so
-	rm -f ${D}${base_libdir}/libnss_files.so
-	rm -f ${D}${base_libdir}/libnss_compat.so
-	rm -f ${D}${base_libdir}/libm.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
-		if [ -e ${D}${base_libdir}/lib${lib}.spec ] ; then
-			mv ${D}${base_libdir}/lib${lib}.spec ${D}${libdir}
-		fi
-		if [ -e ${D}${base_libdir}/lib${lib}.a ] ; then
-			mv ${D}${base_libdir}/lib${lib}.a ${D}${libdir}
-		fi
-		rm -f ${D}${base_libdir}/lib${lib}*
-	done
+	if ${@bb.utils.contains('DISTRO_FEATURES', 'usrmerge', 'false', 'true', d)}; then
+		# remove potential .so duplicates from base_libdir
+		# for all symlinks created above in libdir
+		rm -f ${D}${base_libdir}/librt.so
+		rm -f ${D}${base_libdir}/libcrypt.so
+		rm -f ${D}${base_libdir}/libresolv.so
+		rm -f ${D}${base_libdir}/libnss_hesiod.so
+		rm -f ${D}${base_libdir}/libutil.so
+		rm -f ${D}${base_libdir}/libBrokenLocale.so
+		rm -f ${D}${base_libdir}/libpthread.so
+		rm -f ${D}${base_libdir}/libthread_db.so
+		rm -f ${D}${base_libdir}/libanl.so
+		rm -f ${D}${base_libdir}/libdl.so
+		rm -f ${D}${base_libdir}/libnss_db.so
+		rm -f ${D}${base_libdir}/libnss_dns.so
+		rm -f ${D}${base_libdir}/libnss_files.so
+		rm -f ${D}${base_libdir}/libnss_compat.so
+		rm -f ${D}${base_libdir}/libm.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
+			if [ -e ${D}${base_libdir}/lib${lib}.spec ] ; then
+				mv ${D}${base_libdir}/lib${lib}.spec ${D}${libdir}
+			fi
+			if [ -e ${D}${base_libdir}/lib${lib}.a ] ; then
+				mv ${D}${base_libdir}/lib${lib}.a ${D}${libdir}
+			fi
+			rm -f ${D}${base_libdir}/lib${lib}*
+		done
 
-	# Clean up duplicate libs that are both in base_libdir and libdir
-	rm -f ${D}${libdir}/libgcc*
+		# Clean up duplicate libs that are both in base_libdir and libdir
+		rm -f ${D}${libdir}/libgcc*
+	fi
 
 	# Besides ld-${EAT_VER_LIBC}.so, other libs can have duplicates like lib*-${EAT_VER_LIBC}.so
 	# Only remove them if both are regular files and are identical