ClangPdbToolChain.py: Update PATH search design

[Antaeus Kleinert-Strand (antklein)]

Description

• Replace manual PATH traversal with shutil.which() for reliable Clang discovery.
• Resolve symlinks so CLANG_BIN points to the actual Clang binary directory. This prevents builds from using a symlink directory that may not contain related LLVM tools required by the toolchain.
• Clean up imports, formatting, and comments for Python style compliance.

• Impacts functionality?
• Impacts security?
• Breaking change?
• Includes tests?
• Includes documentation?

How This Was Tested

• Verified Clang discovery when clang is exposed through a symlink on PATH.
• Confirmed CLANG_BIN resolves to the real LLVM binary directory.
• Confirmed Clang version detection and a CLANGPDB build still succeed.

Integration Instructions

N/A

[Antaeus Kleinert-Strand (antklein)]

release/202608 targeted change for #1910
Aaron (@apop5) FYI

[mu-automation]

❌ QEMU Validation Failed

Source Dependencies

Repository	Commit
mu_basecore	c527eb1
mu_tiano_platforms	d966ff0

Results

Platform	Target	Build	Boot	Overall Boot Time	Build Logs	Boot Logs
Q35	DEBUG	❌ failure	⏩ skipped	N/A	Build Logs	N/A
ArmVirt	DEBUG	❌ failure	⏩ skipped	N/A	Build Logs	N/A

Workflow run: https://github.com/microsoft/mu_basecore/actions/runs/34905590282

This comment was automatically generated by the Mu QEMU PR Validation workflow.

[Codecov Comments Bot (codecov-commenter)]

Codecov Report

✅ All modified and coverable lines are covered by tests.
⚠️ Please upload report for BASE (release/202608@8504428). Learn more about missing BASE report.

Additional details and impacted files

@@                Coverage Diff                @@
##             release/202608    #1917   +/-   ##
=================================================
  Coverage                  ?    1.70%           
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  Files                     ?     1674           
  Lines                     ?   417227           
  Branches                  ?        0           
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  Hits                      ?     7121           
  Misses                    ?   410106           
  Partials                  ?        0           

Flag	Coverage Δ
FmpDevicePkg	8.54% <ø> (?)
MdeModulePkg	0.89% <ø> (?)
MdePkg	4.84% <ø> (?)
NetworkPkg	0.50% <ø> (?)
PolicyServicePkg	28.75% <ø> (?)
SecurityPkg	1.46% <ø> (?)
StandaloneMmPkg	0.47% <ø> (?)
UefiCpuPkg	4.17% <ø> (?)
UnitTestFrameworkPkg	16.29% <ø> (?)

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[Antaeus Kleinert-Strand (antklein)]

Abandoning in favor of cherry-picking this edk2 PR once it completes. tianocore/edk2#12502