bug#15675: the configure script invoked before make

[Glenn Morris]

Eli Zaretskii wrote:

> (MinGW needs the test programs to pick up headers in nt/inc, since
> those headers define some stuff which is not available in the MinGW
> system headers.  This is what GCC_TEST_OPTIONS are for, right?)

I don't really know what *GCC_TEST_OPTIONS is for.
The only thing in configure using it apart from MinGW is Irix,
which frankly is used by ~ no-one.

Emacs autoconf usage is not always best-practice...
It seems to me that both the Irix and MinGW cases should be using
C(PP)FLAGS instead of using GCC_TEST_OPTIONS to modify CC.