`src/time/time_utils.h` unconditionally uses `EOVERFLOW`

[petrhosek]

Including time.h entrypoints such as asctime, gmtime or mktime results in a compile error:

In file included from /usr/local/google/home/phosek/llvm/llvm-project/libc/src/time/asctime.cpp:11:
/usr/local/google/home/phosek/llvm/llvm-project/libc/src/time/time_utils.h:94:16: error: use of undeclared identifier 'EOVERFLOW'                                                                                    
   94 |   libc_errno = EOVERFLOW;                                                                                                                                                                                    
      |                ^                                                                                  
1 error generated.

This is because src/time/time_utils.h unconditionally uses EOVERFLOW which is only defined in POSIX and not in C standard, but we're trying to avoid including POSIX in baremetal environments. More generally, I don't think that functions defined by the C standard should have unconditional dependencies on POSIX.

CC @michaelrj-google

[llvmbot]

@llvm/issue-subscribers-libc

Author: Petr Hosek (petrhosek)

Including `time.h` entrypoints such as `asctime`, `gmtime` or `mktime` results in a compile error: ``` In file included from /usr/local/google/home/phosek/llvm/llvm-project/libc/src/time/asctime.cpp:11: /usr/local/google/home/phosek/llvm/llvm-project/libc/src/time/time_utils.h:94:16: error: use of undeclared identifier 'EOVERFLOW' 94 | libc_errno = EOVERFLOW; | ^ 1 error generated. ``` This is because `src/time/time_utils.h` [unconditionally uses `EOVERFLOW`](https://github.com/llvm/llvm-project/blob/89b7b3b9952210fbd9bd0db95385bfed69ffc7a3/libc/src/time/time_utils.h#L94) which is only defined in POSIX and not in C standard, but we're trying to avoid including POSIX in baremetal environments. More generally, I don't think that functions defined by the C standard should have unconditional dependencies on POSIX.

CC @michaelrj-google