[libc] Add printf error handling (with fixes)

[mleleszi]

#159474

Resubmitting #162876 with fixes as it broke some buildbots:

• Fix comparisons of integer expressions of different signedness
• Not check for specific errnos in tests, as they might not be available on all platforms

[mleleszi]

@michaelrj-google

[michaelrj-google]

LGTM, I'm going to run some tests locally before merging

[michaelrj-google]

this needs to be fixed. Was preventing the tests from running.

Suggested change

	if(NOT TARGET ${target_error_converter})
	if(NOT TARGET ${target_error_mapper})

[mleleszi]

Good catch! Actually there was an issue with a test that didn't run, had to change %n in the nullptr check test case for fprintf, as I was trying to test write_int_converter.h#L29, not the string conversion. Added a guard for LIBC_COPT_PRINTF_DISABLE_WRITE_INT

[michaelrj-google]

Tests seem clean, merging now and I'll keep an eye on the buildbots.

[llvm-ci]

LLVM Buildbot has detected a new failure on builder openmp-offload-amdgpu-runtime-2 running on rocm-worker-hw-02 while building libc at step 10 "Add check check-libc-amdgcn-amd-amdhsa".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/10/builds/16688

Here is the relevant piece of the build log for the reference

Step 10 (Add check check-libc-amdgcn-amd-amdhsa) failure: test (failure)
...
[ RUN      ] LlvmLibcStrtoimaxTest.DecodeInOtherBases
[       OK ] LlvmLibcStrtoimaxTest.DecodeInOtherBases (340 ms)
[ RUN      ] LlvmLibcStrtoimaxTest.CleanBaseSixteenDecode
[       OK ] LlvmLibcStrtoimaxTest.CleanBaseSixteenDecode (134 us)
[ RUN      ] LlvmLibcStrtoimaxTest.MessyBaseSixteenDecode
[       OK ] LlvmLibcStrtoimaxTest.MessyBaseSixteenDecode (22 us)
[ RUN      ] LlvmLibcStrtoimaxTest.AutomaticBaseSelection
[       OK ] LlvmLibcStrtoimaxTest.AutomaticBaseSelection (41 us)
Ran 7 tests.  PASS: 7  FAIL: 0
[3126/3299] Running hermetic test libc.test.src.stdio.fprintf_test.__hermetic__
FAILED: libc/test/src/stdio/libc.test.src.stdio.fprintf_test.__hermetic__.__cmd__ /home/botworker/builds/openmp-offload-amdgpu-runtime-2/llvm.build/runtimes/runtimes-amdgcn-amd-amdhsa-bins/libc/test/src/stdio/libc.test.src.stdio.fprintf_test.__hermetic__.__cmd__ 
cd /home/botworker/builds/openmp-offload-amdgpu-runtime-2/llvm.build/runtimes/runtimes-amdgcn-amd-amdhsa-bins/libc/test/src/stdio && /home/botworker/builds/openmp-offload-amdgpu-runtime-2/llvm.build/bin/amdhsa-loader /home/botworker/builds/openmp-offload-amdgpu-runtime-2/llvm.build/runtimes/runtimes-amdgcn-amd-amdhsa-bins/libc/test/src/stdio/libc.test.src.stdio.fprintf_test.__hermetic__.__build__
[==========] Running 2 tests from 1 test suite.
[ RUN      ] LlvmLibcFPrintfTest.WriteToFile
/home/botworker/builds/openmp-offload-amdgpu-runtime-2/llvm.src/libc/test/src/stdio/fprintf_test.cpp:86: FAILURE
      Expected: 9
      Which is: 9
To be equal to: static_cast<int>(libc_errno)
      Which is: 0
[  FAILED  ] LlvmLibcFPrintfTest.WriteToFile
[ RUN      ] LlvmLibcFPrintfTest.NullPtrCheck
/home/botworker/builds/openmp-offload-amdgpu-runtime-2/llvm.src/libc/test/src/stdio/fprintf_test.cpp:102: FAILURE
       Expected: ret
       Which is: 8
To be less than: 0
       Which is: 0
/home/botworker/builds/openmp-offload-amdgpu-runtime-2/llvm.src/libc/test/src/stdio/fprintf_test.cpp:103: FAILURE
      Expected: 22
      Which is: 22
To be equal to: static_cast<int>(libc_errno)
      Which is: 0
[  FAILED  ] LlvmLibcFPrintfTest.NullPtrCheck
Ran 2 tests.  PASS: 0  FAIL: 2
[3127/3299] Running hermetic test libc.test.src.stdio.printf_test.__hermetic__
[==========] Running 1 test from 1 test suite.
[ RUN      ] LlvmLibcPrintfTest.PrintOut
[       OK ] LlvmLibcPrintfTest.PrintOut (137 us)
Ran 1 tests.  PASS: 1  FAIL: 0
A simple string with no conversions.
1234567890
1234 and more
[3128/3299] Linking CXX executable libc/test/src/stdio/libc.test.src.stdio.sscanf_test.__hermetic__.__build__
[3129/3299] Running hermetic test libc.test.src.inttypes.strtoumax_test.__hermetic__
[==========] Running 7 tests from 1 test suite.
[ RUN      ] LlvmLibcStrtoumaxTest.InvalidBase
[       OK ] LlvmLibcStrtoumaxTest.InvalidBase (8 us)
[ RUN      ] LlvmLibcStrtoumaxTest.CleanBaseTenDecode
[       OK ] LlvmLibcStrtoumaxTest.CleanBaseTenDecode (101 us)
[ RUN      ] LlvmLibcStrtoumaxTest.MessyBaseTenDecode