Wishlist: Support user build flags

[d-torrance]

There are some standard variables (CPPFLAGS, CFLAGS, CXXFLAGS, and LDFLAGS) that are frequently set by users to pass build flags to compilers. For example, Debian uses them for hardening binaries in its packages.

It would be great if support for these variables be could be added. For gprbuild, the following works for C code:

        for Default_Switches ("C") use External_As_List ("CPPFLAGS", " ") &
            External_As_List ("CFLAGS", " ");

[zhangyusi-hub]

Hello, I want to ask you two problems about the gnat compilers.
I used the following method to compile the makefile in /PHCpack/src/MPI:
cd /PHCpack/src/MPI
make all

But there is a following error with gnatbind: invalid switch: -C
gcc -c call_hello.c
gnatmake -c hello.adb
gnatmake: objects up to date.
gnatbind -n -C hello
gnatbind: invalid switch: -C

And when I modify it with gnatbind -n -c hello, there is another error with gnatlink: Failed to open binder output:
gcc -c call_hello.c
gnatmake -c hello.adb
gnatmake: objects up to date.
gnatbind -n -c hello
gnatlink -c hello call_hello.o adatest.o -o adatest
--LINK=/BIGDATA1/app/MPI/mpich/3.2.1-gcc-4.8.5-dynamic/bin/mpicc
gnatlink: Failed to open binder output
Could you tell me how to solve the two problems about the compile commands gnatbind and gnatlink ？