autoconf: detect libcrypto with PKG_CHECK_MODULES

I'm trying to compile on win32, using a static openssl.
When linking against libcryto on win32, "-lws2_32 -lgdi32 -lcrypt32" should be added to LD_FLAGS for the link to work
The lib detection fail in ./configure because of symbol missing
Using PKG_CONFIG in configure correct this problem

I didn't commit aclocal and configure, so "aclocal" and 'autoconf" should be run in order to make the change effective