ci: Recognize more CI_ variables for better cross-platform verification

For ci_autotools.sh, customize CPP, CPPFLAGS, AR, RANLIB, LD, LDFLAGS
via CI_CPP, CI_CPP_FLAGS, CI_AR, CI_RANLIB, CI_LD, CI_LD_FLAGS.

For ci_cmake.sh and ci_legacy.sh, customize AR, AR_RC and RANLIB via
CI_AR and CI_RANLIB.

Rewrite portions of ci_legacy.sh to match the style of ci_cmake.sh.
3 files changed