clang llvm build error with -save-temps=obj

[Chrys4lisfag]

Description

Passing save temps for cpr target breaks the compilation
1:

CMake Error at cmake-build-relwithdebinfo-clang/_deps/cpr-src/include/CMakeLists.txt:95 (message):
  Your compiler does not support the `<filesystem>` include or cpr is unable
  to determine the proper compiler flags for it.

2. Due to set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -Wextra -Wpedantic -Werror")
   error: this style of line directive is a GNU extension [-Werror,-Wgnu-line-marker]

After crutching these two issues by forcing STD_FS_SUPPORTED and removing -Werror it compiled successfully

Example/How to Reproduce

set these flags:
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -save-temps=obj -flto")
set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -save-temps=obj -flto")

issue repo:
https://github.com/Chrys4lisfag/cpr-llvm-issue

Possible Fix

No response

Where did you get it from?

GitHub (branch e.g. master)

Additional Context/Your Environment

• OS: Windows
• Version: master
• clang-llvm 21