Warn the build isn't going to be portable when FASTR_RELEASE=dev

mx.fastr/mx_copylib.py

@@ -133,7 +133,10 @@ def copylib(args):
 #        if args[0] == 'quadmath' and (mx.get_arch() == 'sparcv9' or mx.get_os() == 'solaris'):
         if mx.get_arch() == 'sparcv9' or mx.get_os() == 'solaris':
             return 0
-        if os.environ.get('FASTR_RELEASE') != 'dev':
+        if os.environ.get('FASTR_RELEASE') == 'dev':
+            mx.log(args[0] + ' not found in PKG_LDFLAGS_OVERRIDE, but required with FASTR_RELEASE')
+            mx.log('the resulting FastR release build will not be portable to another system')
+        else:
             mx.abort(args[0] + ' not found in PKG_LDFLAGS_OVERRIDE, but required with FASTR_RELEASE')
 
     mx.log(args[0] + ' not found in PKG_LDFLAGS_OVERRIDE, assuming system location')