In ax_harden_compiler_flags.m4, a couple of the AC_REQUIRE macros were being used to check for the presence of another macro. Replaced them with uses of AX_REQUIRE_DEFINED which checks for the presence of a macro. AC_REQUIRE ensures a macro is expanded.
1. Update several of the macro files paralleling wolfSSL's m4 files.
2. Check the ar options and if available add the "U" options.
3. Add the -Xcompiler flag ahead of -Qunused-arguments for -pthreads.