[m-rev.] for review: Fix detection of MinGW-w64 gcc version.

[Julien Fischer]

On Thu, 3 May 2018, Peter Wang wrote:

> The MinGW-w64 port of gcc may report a version like "7.3-win32" or
> "7.3-posix". Our gcc version detection code did not expect the
> suffixes so would extract "3-win32" or "3-posix" as the minor version.
>
> m4/mercury.m4:
>    Ignore a "-suffix" in the output of gcc -dumpversion.

That's fine.

Julien.