Make mk1mf.pl aware of configure.mk
Create top-level build.mk
Update Makefiles to include configure.mk
Include configure.mk in Makefile.shared
Move DIRS and related vars to configure.mk.org
Strip variables in configure.mk from build.mk
Eliminate CLEARENV after configure.mk migration
Move more Makefile variables into configure.mk
Add MAKEFILE and MAKEOVERRIDES to configure.mk.org.
Remove more configure.mk variables from build.mk
Fix CC in FIPS_BUILD_CMD and FIPS_CRYPTO_BUILD_CMD

This should have been $(CC) all along; removing $(BUILDENV) from the
make invocation causes ${{CC}} to be empty, thanks to 'make -e', triggering a
build failure as LDCMD receives no value.
Eliminate BUILDENV after configure.mk migration