Fix missing null terminator in runtime path resolution on Linux

[aeu]

readlink does not null terminate the output buffer. The existing code passed the full buffer size to readlink, which did not leave any space to append a terminator.

This change passes size -1 to readlink and terminates the buffer with a '\0' after a successful read to avoid reading past the end of the buffer.

This change is consistent with the usage pattern seen in swift-foundation-icu / icuSources / common / putil.cpp

[al45tair]

@swift-ci Please smoke test

[aeu]

@al45tair - Hello. I am seeing that the smoke tests failed, but looking at the console output it looks like the failures are unrelated to my changes.

What do I need to do to proceed here?

Thanks.

[al45tair]

Looks like we just need to re-trigger them.

[al45tair]

@swift-ci Please smoke test

[aeu]

@al45tair

One of the smoke tests (for windows) failed, on the following:

[342/389][ 87%][352.140s] Linking CXX shared library bin\swiftObservation.dll
FAILED: bin/swiftObservation.dll lib/swift/windows/aarch64/swiftObservation.lib 
C:\Windows\system32\cmd.exe /C "cd . && "C:\Program Files\CMake\bin\cmake.exe" -E vs_link_dll --intdir=stdlib\public\Observation\Sources\Observation\CMakeFiles\swiftObservation-windows-aarch64.dir --rc=C:\PROGRA~2\WI3CF2~1\10\bin\100226~1.0\x64\rc.exe --mt=C:\PROGRA~2\WI3CF2~1\10\bin\100226~1.0\x64\mt.exe --manifests  -- T:\5\bin\lld-link.exe /nologo stdlib\public\Observation\Sources\Observation\WINDOWS\aarch64\Observation.obj lib\swift\windows\aarch64\swiftrt.obj stdlib\public\Observation\Sources\Observation\CMakeFiles\swiftObservation-windows-aarch64.dir\ThreadLocal.cpp.obj  /out:bin\swiftObservation.dll /implib:lib\swift\windows\aarch64\swiftObservation.lib /pdb:bin\swiftObservation.pdb /dll /version:0.0 /INCREMENTAL:NO /OPT:REF /OPT:ICF /INCREMENTAL:NO -LIBPATH:T:\aarch64-unknown-windows-msvc\LLVM\.\lib   -LIBPATH:T:\aarch64-unknown-windows-msvc\Runtime\.\lib\swift\windows\aarch64   -LIBPATH:T:\5\bin\..\lib\swift\windows\aarch64   -LIBPATH:T:\5\bin\..\lib\swift\windows   -LIBPATH:\\usr\lib\swift   -LIBPATH:T:\aarch64-unknown-windows-msvc\Runtime\winsdk_lib_aarch64_symlinks lib\swift\windows\aarch64\swift_Concurrency.lib  lib\swift\windows\aarch64\swiftCore.lib  kernel32.lib user32.lib gdi32.lib winspool.lib shell32.lib ole32.lib oleaut32.lib uuid.lib comdlg32.lib advapi32.lib && cd ."
LINK: command "T:\5\bin\lld-link.exe /nologo stdlib\public\Observation\Sources\Observation\WINDOWS\aarch64\Observation.obj lib\swift\windows\aarch64\swiftrt.obj stdlib\public\Observation\Sources\Observation\CMakeFiles\swiftObservation-windows-aarch64.dir\ThreadLocal.cpp.obj /out:bin\swiftObservation.dll /implib:lib\swift\windows\aarch64\swiftObservation.lib /pdb:bin\swiftObservation.pdb /dll /version:0.0 /INCREMENTAL:NO /OPT:REF /OPT:ICF /INCREMENTAL:NO -LIBPATH:T:\aarch64-unknown-windows-msvc\LLVM\.\lib -LIBPATH:T:\aarch64-unknown-windows-msvc\Runtime\.\lib\swift\windows\aarch64 -LIBPATH:T:\5\bin\..\lib\swift\windows\aarch64 -LIBPATH:T:\5\bin\..\lib\swift\windows -LIBPATH:\\usr\lib\swift -LIBPATH:T:\aarch64-unknown-windows-msvc\Runtime\winsdk_lib_aarch64_symlinks lib\swift\windows\aarch64\swift_Concurrency.lib lib\swift\windows\aarch64\swiftCore.lib kernel32.lib user32.lib gdi32.lib winspool.lib shell32.lib ole32.lib oleaut32.lib uuid.lib comdlg32.lib advapi32.lib /MANIFEST:EMBED,ID=2" failed (exit code 1) with the following output:
lld-link: error: could not open 'swiftWinSDK.lib': no such file or directory

This looks like it's an issue with the environment of the smoke test itself, but I don't know how to dig deeper on this.

[al45tair]

@aeu This is an unrelated failure, and it's affecting everyone I think. I'll chase it up.

[al45tair]

This looks like a dependency graph problem; I think we'll need #85454 to fix it.

[al45tair]

@swift-ci Please smoke test Windows platform

[aeu]

@al45tair - I see that #85454 was merged, but it looks there is still an issue with the Windows test suite. I took a look at the logs, but I don't have the background to diagnose the issue.

[al45tair]

@swift-ci Please smoke test Windows platform

[aeu]

@al45tair - clean smoke test, looks like the fixes to the Windows test suite worked.