cpr: add pic and shared variants

[prudhomm]

Summary

This issue proposes adding two new variants, +pic and +shared, to the cpr package in Spack:

• +pic: Enables building position-independent code (PIC) for static libraries, useful for linking into shared libraries.
• +shared: Controls whether to build cpr as a shared or static library.

Rationale

1. Position-Independent Code (+pic): Building position-independent code (PIC) is essential for linking static libraries into shared libraries. Currently, cpr only builds static libraries, which restricts its usability in applications that need to link with PIC-compatible code. By adding a +pic variant, users have the option to enable PIC, improving cpr’s compatibility with larger projects and shared library requirements.
2. Shared Libraries (+shared): The default static library build limits flexibility, as many projects require shared libraries to manage memory and dependencies more effectively. Adding a +shared variant allows users to choose between static and shared library builds, making cpr more versatile and better suited for dynamic linking needs in complex projects.

Description

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Additional information

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General information

• I have searched the issues of this repo and believe this is not a duplicate