Processing GNU-style "make variables" - implementation

Support the following "make variables":

AR              (GNU compatible)
ARFLAGS         (GNU Compatible)
AS              (GNU Compatible)
ASFLAGS         (GNU Compatible)
CC              (GNU Compatible)
CFLAGS          (GNU Compatible)
CXX             (GNU Compatible)
CXXFLAGS        (GNU Compatible)
CPP             (GNU Compatible)
CPPFLAGS        (GNU Compatible)
CPPDEFINES      List of CPP macro definitions.  Alternative for -D
CPPINCLUDES     List of CPP inclusion directories.  Alternative for -I
HASHBANGPERL    Perl invocation to be inserted after '#!' in public
                perl scripts.
LDFLAGS         (GNU Compatible)
LDLIBS          (GNU Compatible)
RANLIB          Program to generate library archive index
RC              Program to manipulate Windows resources
RCFLAGS         Flags for $(RC)
RM              (GNU Compatible)

Setting one of these overrides the corresponding data from our config
targets.  However, flags given directly on the configuration command
line are additional, and are therefore added to the flags coming from
one of the variables above or the config target.

Fixes #2420

Reviewed-by: Tim Hudson <tjh@openssl.org>
Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/5177)