libtool: fix empty "-L" in compiler_lib_search_path

If the compiler places a space between "-L" and the path, the path will
be skipped and only an empty "-L" will appear in the final
compiler_lib_search_path. This will cause the first library in postdeps
following compiler_lib_search_path to be accidentally skipped.

* libtool.m4: Fixed string comparison by adding missing 'x's.

m4/libtool.m4

@@ -7563,8 +7563,8 @@ if AC_TRY_EVAL(ac_compile); then
     -L* | -R* | -l*)
        # Some compilers place space between "-{L,R}" and the path.
        # Remove the space.
-       if test x-L = "$p" ||
-          test x-R = "$p"; then
+       if test x-L = x"$p" ||
+          test x-R = x"$p"; then
 	 prev=$p
 	 continue
        fi