[libc][tests] make unit tests hermetic

[RossComputerGuy]

Tracking issue to keep track of tests aren't hermetic

• [libc] port fpe and process-related unit test utils to hermetic mode #133925
• [libc][test] libc/test/UnitTest/RoundingModeUtils.cpp is not hermetic #135211
• [libc][test] libc/test/UnitTest/LibcTestMain.cpp should be hermetic #135213
• [libc][test] libc/test/UnitTest/LibcTest.cpp should be hermetic #135214
• [libc][test] libc/test/UnitTest/TestLogger.cpp should be hermetic #135215
• [libc][test] libc/test/UnitTest/MemoryMatcher.cpp should be hermetic #135216
• [libc][test] libc/test/UnitTest/CmakeFilePath.cpp should be hermetic #135217

[llvmbot]

@llvm/issue-subscribers-libc

Author: Tristan Ross (RossComputerGuy)

Tracking issue to keep track of tests aren't hermetic

• #133925
• #135211
• #135213
• #135214
• #135215
• #135216
• #135217