Ensure Windows paths used by CMake contain forward slashes only

CMake will fail if the toolchain fail generated by rules_foreign_cc
contains backslashes.

foreign_cc/private/cmake_script.bzl

@@ -349,7 +349,9 @@ def _tail_if_starts_with(str, start):
 def _absolutize(workspace_name, text, force = False):
     if text.strip(" ").startswith("C:") or text.strip(" ").startswith("c:"):
         return text
-    return absolutize_path_in_str(workspace_name, "$$EXT_BUILD_ROOT$$/", text, force)
+
+    # Use bash parameter substitution to replace backslashes with forward slashes as CMake fails if provided paths containing backslashes
+    return absolutize_path_in_str(workspace_name, "$${EXT_BUILD_ROOT//\\\\//}$$/", text, force)
 
 def _join_flags_list(workspace_name, flags):
     return " ".join([_absolutize(workspace_name, flag) for flag in flags])

test/cmake_text_tests.bzl

@@ -12,12 +12,12 @@ def _absolutize_test(ctx):
     env = unittest.begin(ctx)
 
     cases = {
-        "-Lexternal/cmake/aaa": "-L$$EXT_BUILD_ROOT$$/external/cmake/aaa",
+        "-Lexternal/cmake/aaa": "-L$${EXT_BUILD_ROOT//\\\\//}$$/external/cmake/aaa",
         "/abs/a12": "/abs/a12",
         "abs/a12": "abs/a12",
-        "external/cmake/aaa": "$$EXT_BUILD_ROOT$$/external/cmake/aaa",
-        "name=ws/cmake/aaa": "name=$$EXT_BUILD_ROOT$$/ws/cmake/aaa",
-        "ws/cmake/aaa": "$$EXT_BUILD_ROOT$$/ws/cmake/aaa",
+        "external/cmake/aaa": "$${EXT_BUILD_ROOT//\\\\//}$$/external/cmake/aaa",
+        "name=ws/cmake/aaa": "name=$${EXT_BUILD_ROOT//\\\\//}$$/ws/cmake/aaa",
+        "ws/cmake/aaa": "$${EXT_BUILD_ROOT//\\\\//}$$/ws/cmake/aaa",
     }
 
     for case in cases:
@@ -94,11 +94,11 @@ def _fill_crossfile_from_toolchain_test(ctx):
     expected = {
         "CMAKE_AR": "/cxx_linker_static",
         "CMAKE_ASM_FLAGS_INIT": "assemble",
-        "CMAKE_CXX_COMPILER": "$$EXT_BUILD_ROOT$$/external/cxx-value",
+        "CMAKE_CXX_COMPILER": "$${EXT_BUILD_ROOT//\\\\//}$$/external/cxx-value",
         "CMAKE_CXX_COMPILER_EXTERNAL_TOOLCHAIN": "cxx-toolchain",
         # Quoted args are escaped when crossfile is written to a script in create_cmake_script
         "CMAKE_CXX_FLAGS_INIT": "--quoted=\"abc def\" --sysroot=/abc/sysroot --gcc_toolchain cxx-toolchain",
-        "CMAKE_CXX_LINK_EXECUTABLE": "$$EXT_BUILD_ROOT$$/ws/cxx_linker_executable <FLAGS> <CMAKE_CXX_LINK_FLAGS> <LINK_FLAGS> <OBJECTS> -o <TARGET> <LINK_LIBRARIES>",
+        "CMAKE_CXX_LINK_EXECUTABLE": "$${EXT_BUILD_ROOT//\\\\//}$$/ws/cxx_linker_executable <FLAGS> <CMAKE_CXX_LINK_FLAGS> <LINK_FLAGS> <OBJECTS> -o <TARGET> <LINK_LIBRARIES>",
         "CMAKE_C_COMPILER": "/some-cc-value",
         "CMAKE_C_COMPILER_EXTERNAL_TOOLCHAIN": "cc-toolchain",
         "CMAKE_C_FLAGS_INIT": "-cc-flag -gcc_toolchain cc-toolchain",