Fix Windows static monolithic builds

[tylerm-nv]

Description of Change(s)

Ensures that TARGET_PDB_FILE is only used on shared builds since linker artifacts are required, and static builds only produce compiler artifacts. The monolithic build is missing this guard.

Fixes Issue(s)

Fixes cmake error during static monolithic builds on Windows.

python3 ./build_scripts/build_usd.py --build-monolithic --no-imaging --no-python --no-tests --cmake-build-args=-DBUILD_SHARED_LIBS=OFF {install_dir}

Error fixed by change:

CMake Error:
  Error evaluating generator expression:
    $<TARGET_PDB_FILE:usd_m>
  TARGET_PDB_FILE is allowed only for targets with linker created artifacts.

Checklist

• I have created this PR based on the dev branch

• I have followed the coding conventions

• I have added unit tests that exercise this functionality (Reference:
  testing guidelines)

• I have verified that all unit tests pass with the proposed changes

• I have submitted a signed Contributor License Agreement (Reference:
  Contributor License Agreement instructions)

[jesschimein]

Filed as internal issue #USD-11685

(This is an automated message. See here for more information.)