PKG_CHECK_MODULES for msgpack and jansson

Using AS_IF rather than shell "if" is recommended for conditionals
that contain non-trivial autoconf macros, because autoconf will emit
any AC_REQUIREd autoconf macro expansions outside of the conditional.
This makes them available elsewhere in the configure script.

binutils/
	* configure.ac (msgpack): Use "AS_IF" rather than "if".
	* configure: Regenerate.
ld/
	* configure.ac (jansson): Use "AS_IF" rather than "if".
	* configure: Regenerate.