+ The following variables are used as "make variables" and
+ can be used as an alternative to giving preprocessor,
+ compiler and linker options directly as configuration.
+ The following variables are supported:
+
+ AR The static library archiver.
+ ARFLAGS Flags for the static library archiver.
+ AS The assembler compiler.
+ ASFLAGS Flags for the assembler compiler.
+ CC The C compiler.
+ CFLAGS Flags for the C compiler.
+ CXX The C++ compiler.
+ CXXFLAGS Flags for the C++ compiler.
+ CPP The C/C++ preprocessor.
+ CPPFLAGS Flags for the C/C++ preprocessor.
+ CPPDEFINES List of CPP macro definitions, separated
+ by a platform specific character (':' or
+ space for Unix, ';' for Windows, ',' for
+ VMS). This can be used instead of using
+ -D (or what corresponds to that on your
+ compiler) in CPPFLAGS.
+ CPPINCLUDES List of CPP inclusion directories, separated
+ the same way as for CPPDEFINES. This can
+ be used instead of -I (or what corresponds
+ to that on your compiler) in CPPFLAGS.
+ HASHBANGPERL Perl invocation to be inserted after '#!'
+ in public perl scripts (only relevant on
+ Unix).
+ LD The program linker (not used on Unix, $(CC)
+ is used there).
+ LDFLAGS Flags for the shared library, DSO and
+ program linker.
+ LDLIBS Extra libraries to use when linking.
+ Takes the form of a space separated list
+ of library specifications on Unix and
+ Windows, and as a comma separated list of
+ libraries on VMS.
+ RANLIB The library archive indexer.
+ RC The Windows resource compiler.
+ RCFLAGS Flags for the Windows resource compiler.
+ RM The command to remove files and directories.
+
+ These cannot be mixed with compiling / linking flags given
+ on the command line. In other words, something like this
+ isn't permitted.
+
+ ./config -DFOO CPPFLAGS=-DBAR -DCOOKIE
+
+ 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
+
+ If CC is set, it is advisable to also set CXX to ensure
+ both C and C++ compilers are in the same "family". This
+ becomes relevant with 'enable-external-tests' and
+ 'enable-buildtest-c++'.
+