cmake: fix a redundant flag causing the build to fail with newer GCC versions

[SquareRobin]

Summary

Passing -D_GLIBCXX_ASSERTIONS directly to the preprocessor results in an error compiling with GCC 14 or 15 (14.3.1 and 15.3.0) , simply removing -Wp fixes this and causes no compile time errors/warnings. Tests also pass with the flag changed.

Type of Change

• Bug fix

Impact

Adds support for GCC 14 and 15 (probably other versions, too) while causing no observable functionality changes.

Verification

• I have verified that the local build succeeds (ran cmake manually).
• I have run the relevant tests and they pass.
• My code follows the repository's formatting guidelines.
• I have signed my commits (DCO).

[gemini-code-assist]

Code Review

This pull request updates the compiler options in src/CMakeLists.txt by changing -Wp,-D_GLIBCXX_ASSERTIONS to -D_GLIBCXX_ASSERTIONS. The reviewer recommended wrapping this macro in a C++ generator expression to ensure it is only applied to C++ source files and not C or assembly files.

[gemini-code-assist]

Since _GLIBCXX_ASSERTIONS is a C++ standard library (libstdc++) specific macro, it is best practice to restrict it to C++ compilation using a generator expression. This prevents the flag from being passed to C or assembly source files in the project (such as those in subdirectories like ABC or linenoise).

  $<$<COMPILE_LANGUAGE:CXX>:-D_GLIBCXX_ASSERTIONS>

[github-actions]

Welcome to OpenROAD! Thanks for opening your first PR.
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• CI passes
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