The Tru64 native compiler parses the "-Wno-unused" flag as '-W' (pass arguments
to compiler passes denoted by the letters 'n', 'o', 'u', 's', 'e', 'd').  When
the configure script compiles the "int main(void) { return 0; }" test program
(using "cc -Wno-unused -c conftest.c"), it is successful.

As a result, configure assumes the compiler will accept the "-Wno-unused" flag.

However, when actually generating an executable, the Tru64 native compiler fails
and spits out the error:

> Invalid flag usage: Wno-unused, -Wx,-option must appear after -_SYSTYPE_SVR4
> ld: Usage: ld [options] file [...]

The fix here is to ask the configure script to generate an executable -- which
will fail on Tru64 -- so that it is discovered that the Tru64 compiler does not
really accept the "-Wno-unused" flag.

The only configure script that checks for "-Wno-unused" is in
"source-trees/ws-gram/client/c/source/configure.in".  For this package, I've
included a patch that requires an executable be generated.  That is, I've
changed the test compile from:

   $CC -Wno-unused -c conftest.c

to:

   $CC -Wno-unused conftest.c -o conftest

(and then remove both "conftest.c" and "conftest" afterward).