VMS: Use different C flags for programs that aren't to be installed

This is generalised by having the following macros for stuff that won't
be installed:

    NO_INST_LIB_CFLAGS, used instead of LIB_CFLAGS
    NO_INST_DSO_CFLAGS, used instead of DSO_CFLAGS
    NO_INST_BIN_CFLAGS, used instead of BIN_CFLAGS

They take values from corresponding target config fields if those are
defined, otherwise they take the respective values from LIB_CFLAGS,
DSO_CFLAGS and BIN_CFLAGS.

Reviewed-by: Rich Salz <rsalz@openssl.org>