configure: Detect Solaris libc in an OpenIndiana/illumos compatible way

configure

@@ -3437,7 +3437,7 @@ probe_libc(){
         eval ${pfx}libc_type=klibc
     elif check_${pfx}cpp_condition sys/cdefs.h "defined __BIONIC__"; then
         eval ${pfx}libc_type=bionic
-    elif check_${pfx}cpp_condition sys/brand.h "defined SOLARIS_BRAND_NAME"; then
+    elif check_${pfx}cpp_condition sys/brand.h "defined LABELED_BRAND_NAME"; then
         eval ${pfx}libc_type=solaris
         add_${pfx}cppflags -D__EXTENSIONS__ -D_XOPEN_SOURCE=600
     fi