[clang] [test] Skip a test that sets PATH= on Windows

The same has been done in a couple other existing tests, that also
are skipped on Windows (e.g. ld-path.c). Some tests that really
do want to test setting the path on Windows does it differently,
see e.g. ps4-ps5-linker-win.c.

Since a65771f, the spirv-toolchain.cl
test does one test where PATH is set. Setting PATH does work in
some build configurations - however, if built with e.g. llvm-mingw,
the built Clang executable depends on libc++.dll (and libunwind.dll)
which are found in PATH. If the PATH is overridden, the newly built
Clang executable no longer can run.

Split the test that requires setting PATH to a separate file,
and mark it as unsupported on Windows.

Author: mstorsjo

clang/test/Driver/spirv-toolchain-version.cl

@@ -0,0 +1,14 @@
+/// This test uses the PATH environment variable; on Windows, we may need to retain
+/// the original path for the built Clang binary to be able to execute (as it is
+/// used for locating dependent DLLs).
+// UNSUPPORTED: system-windows
+
+//-----------------------------------------------------------------------------
+// Check llvm-spirv-<LLVM_VERSION_MAJOR> is used if it is found in PATH.
+// RUN: mkdir -p %t/versioned
+// RUN: touch %t/versioned/llvm-spirv-%llvm-version-major \
+// RUN:   && chmod +x %t/versioned/llvm-spirv-%llvm-version-major
+// RUN: env "PATH=%t/versioned" %clang -### --target=spirv64 -x cl -c %s 2>&1 \
+// RUN:   | FileCheck -DVERSION=%llvm-version-major --check-prefix=VERSIONED %s
+
+// VERSIONED: {{.*}}llvm-spirv-[[VERSION]]

clang/test/Driver/spirv-toolchain.cl

@@ -77,13 +77,3 @@
 
 // XTOR: {{llvm-spirv.*"}}
 // BACKEND-NOT: {{llvm-spirv.*"}}
-
-//-----------------------------------------------------------------------------
-// Check llvm-spirv-<LLVM_VERSION_MAJOR> is used if it is found in PATH.
-// RUN: mkdir -p %t/versioned
-// RUN: touch %t/versioned/llvm-spirv-%llvm-version-major \
-// RUN:   && chmod +x %t/versioned/llvm-spirv-%llvm-version-major
-// RUN: env "PATH=%t/versioned" %clang -### --target=spirv64 -x cl -c %s 2>&1 \
-// RUN:   | FileCheck -DVERSION=%llvm-version-major --check-prefix=VERSIONED %s
-
-// VERSIONED: {{.*}}llvm-spirv-[[VERSION]]