Bruce Mitchener 810e33125b Update how we configure gcc / clang command lines. (#103) ...

* Move clang/gcc options into makefile-header.

This puts all of the shared options into a single place so that
we can easily update it.

* Add -fwrapv to the clang/gcc command lines.

This is a step along the way to fixing interlisp/medley#90.

Enabling `-fwrapv` will let overflow checks that rely upon undefined
behavior to work correctly. Without this, with modern versions of
clang and gcc, the overflow checks in the C code are eliminated
by the compiler, resulting in incorrect behavior on the part of
Maiko.

See the linked bug for details and discussion.

Hopefully, this usage of `-fwrapv` will go away once we're using
the correct compiler builtins to detect and handle overflow
correctly.

2020-12-19 20:16:31 -08:00

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