+ Backward compatibility note:
+
+ To be compatible with older configuration scripts, the
+ environment variables are ignored if compiling / linking
+ flags are given on the command line, except for these:
+
+ AR, CC, CXX, CROSS_COMPILE, HASHBANGPERL, PERL, RANLIB, RC
+ and WINDRES
+
+ For example, the following command will not see -DBAR:
+
+ CPPFLAGS=-DBAR ./config -DCOOKIE
+
+ However, the following will see both set variables:
+
+ CC=gcc CROSS_COMPILE=x86_64-w64-mingw32- \
+ ./config -DCOOKIE
+