Change #define sk_GENERAL_NAME_freefunc for SunPRO C compiler
SunOS: add a note in HowToBuild on pkg-config
The first change is for the OpenSSL SqueakSSL case of openssl 1.0.2,
to fix a type cast ... I think this potentially impacts all openssl 1.0.2 platforms that use --disable-dynamicopenssl but it seems OK (I think/hope).
For the second change this is a "documentation" update to the HowToBuild
"HOWTO" documentation in the build.sunos directory; this has no further impact.