[llvm-rc] [test] Fix the windres-preproc test with other mingw triple forms. NFC.

[mstorsjo]

Summary

When invoking the preprocessor, llvm-windres produces a mingw
triple; if the llvm default target triple is a mingw target, it
is used as is - if not, a mingw style triple is generated.

Relax the testcase, to not strictly require "w64" as vendor (allow
the vendor field to be missing entirely), and allow both
"mingw32" and "windows-gnu" as OS/environment (where both forms are
common, while the latter is the normalized form).

[mati865]

LGTM

[alvinhochun]

Confirmed that this fixes the test on my end, thanks!

llvm/test/tools/llvm-rc/windres-preproc.test

 ; RUN: llvm-windres -### --include-dir %p/incdir1 --include %p/incdir2 "-DFOO1=\\\"foo bar\\\"" -UFOO2 -D FOO3 --preprocessor-arg "-DFOO4=\\\"baz baz\\\"" %p/Inputs/empty.rc %t.res | FileCheck %s --check-prefix=CHECK1
-; CHECK1: {{^}} "clang" "--driver-mode=gcc" "-target" "{{.*}}-w64-mingw32" "-E" "-xc" "-DRC_INVOKED" "{{.*}}empty.rc" "-o" "{{.*}}preproc-{{.*}}.rc" "-I" "{{.*}}incdir1" "-I" "{{.*}}incdir2" "-D" "FOO1=\"foo bar\"" "-U" "FOO2" "-D" "FOO3" "-DFOO4=\"baz baz\""{{$}}
+; CHECK1: {{^}} "clang" "--driver-mode=gcc" "-target" "{{.*}}-{{.*}}{{mingw32|windows-gnu}}" "-E" "-xc" "-DRC_INVOKED" "{{.*}}empty.rc" "-o" "{{.*}}preproc-{{.*}}.rc" "-I" "{{.*}}incdir1" "-I" "{{.*}}incdir2" "-D" "FOO1=\"foo bar\"" "-U" "FOO2" "-D" "FOO3" "-DFOO4=\"baz baz\""{{$}}
 ; RUN: llvm-windres -### --preprocessor "i686-w64-mingw32-gcc -E -DFOO=\\\"foo\\ bar\\\"" %p/Inputs/empty.rc %t.res | FileCheck %s --check-prefix=CHECK2
 ; CHECK2: {{^}} "i686-w64-mingw32-gcc" "-E" "-DFOO=\"foo bar\"" "{{.*}}empty.rc" "-o" "{{.*}}preproc-{{.*}}.rc"{{$}}