Ninja: Restore detection of clang-cl showIncludes prefix

Since commit 8f82e755f3 (Ninja: Fix detection of MSVC showIncludes
prefix in Italian, 2023-01-26, v3.26.0-rc1~20^2) our regex no longer
matches the output from `clang-cl`, which uses a relative path, forward
slashes, and is always in English [1]:

    Note: including file: ./foo.h

Update the regex to match that too.

[1] https://github.com/llvm/llvm-project/blob/llvmorg-16.0.0/clang/lib/Frontend/HeaderIncludeGen.cpp#L102

Co-authored-by: Brad King <[email protected]>

Modules/CMakeDetermineCompilerId.cmake

@@ -1144,7 +1144,7 @@ function(CMAKE_DETERMINE_MSVC_SHOWINCLUDES_PREFIX lang userflags)
     ENCODING AUTO # cl prints in console output code page
     )
   string(REPLACE "\n" "\n  " msg "  ${out}")
-  if(res EQUAL 0 AND "${out}" MATCHES "(^|\n)([^:\n][^:\n]+:[^:\n]*[^: \n][^: \n]:?[ \t]+)[A-Za-z]:\\\\")
+  if(res EQUAL 0 AND "${out}" MATCHES "(^|\n)([^:\n][^:\n]+:[^:\n]*[^: \n][^: \n]:?[ \t]+)([A-Za-z]:\\\\|\\./)")
     set(CMAKE_${lang}_CL_SHOWINCLUDES_PREFIX "${CMAKE_MATCH_2}" PARENT_SCOPE)
     string(APPEND msg "\nFound prefix \"${CMAKE_MATCH_2}\"")
   else()

Tests/RunCMake/Ninja/RunCMakeTest.cmake

@@ -46,6 +46,7 @@ if(WIN32)
   if(RunCMake_MAKE_PROGRAM)
     set(maybe_MAKE_PROGRAM "-DRunCMake_MAKE_PROGRAM=${RunCMake_MAKE_PROGRAM}")
   endif()
+  run_cmake_script(ShowIncludes-437-ClangCl -DshowIncludes=${showIncludes} ${maybe_MAKE_PROGRAM})
   run_cmake_script(ShowIncludes-437-English -DshowIncludes=${showIncludes} ${maybe_MAKE_PROGRAM})
   run_cmake_script(ShowIncludes-437-French -DshowIncludes=${showIncludes} ${maybe_MAKE_PROGRAM})
   run_cmake_script(ShowIncludes-437-German -DshowIncludes=${showIncludes} ${maybe_MAKE_PROGRAM})

Tests/RunCMake/Ninja/ShowIncludes-437-ClangCl-check.cmake

@@ -0,0 +1,3 @@
+# 'clang-cl /showIncludes' prefix.
+set(expect "Note: including file: ")
+include(${CMAKE_CURRENT_LIST_DIR}/ShowIncludes-check.cmake)

Tests/RunCMake/Ninja/ShowIncludes-437-ClangCl-stdout.txt

@@ -0,0 +1 @@
+-- showIncludes='Note: including file: '

Tests/RunCMake/Ninja/ShowIncludes-437-ClangCl.cmake

@@ -0,0 +1,3 @@
+set(CODEPAGE 437)
+set(VSLANG "clang-cl") # Special case for test, not a real VS value.
+include(${CMAKE_CURRENT_LIST_DIR}/ShowIncludes.cmake)

Tests/RunCMake/showIncludes.c

@@ -28,6 +28,14 @@ int main()
   printf("OEM code page: %u\n", GetOEMCP());
   printf("VSLANG: %s\n", vslang);
 
+  // clang-cl (special case for test, not a real VS value).
+  if (strcmp(vslang, "clang-cl") == 0) {
+    if (cp == 437 || cp == 65001) {
+      printf("Note: including file: ./foo.h\n");
+      return 0;
+    }
+  }
+
   // German.
   if (strcmp(vslang, "1031") == 0) {
     if (cp == 437 || cp == 65001) {