feat: Add pkg-config support

[nmandelblit]

Summary

• Added support for generating and installing a .pc file for pkg-config
• Controlled by the SENTRY_INSTALL_PKGCONFIG CMake option
• Uses the existing sentry.pc.in template to generate the pkg-config file
• Installs the generated file to the standard pkg-config directory (${CMAKE_INSTALL_LIBDIR}/pkgconfig)

Benefits

This allows downstream projects to easily discover and link against sentry-native using pkg-config:

pkg-config --cflags --libs sentry

Test plan

• Build with SENTRY_INSTALL_PKGCONFIG enabled
• Verify sentry.pc file is generated in build directory
• Verify sentry.pc file is installed to correct location
• Test that pkg-config can find and use the installed file

[seer-by-sentry]

Potential bug: The pkg-config template hardcodes the library directory to lib, but the actual installation may use lib64 on some systems, causing linker errors.

• Description: The pkg-config template file sentry.pc.in hardcodes the library directory with libdir=${prefix}/lib. However, the actual library installation uses the CMAKE_INSTALL_LIBDIR variable, which resolves to lib64 on many common 64-bit Linux distributions like RHEL, Fedora, and CentOS. This discrepancy causes pkg-config to provide an incorrect library path to downstream projects. As a result, the linker will fail to find the sentry library because it searches in the wrong directory, preventing dependent applications from building successfully on these platforms.

• Suggested fix: The sentry.pc.in template should not hardcode the libdir. Instead, it should be configured by CMake during the build process. Replace the hardcoded libdir=${prefix}/lib line with a placeholder like libdir=@CMAKE_INSTALL_FULL_LIBDIR@. Then, in CMakeLists.txt, use the configure_file command to substitute this placeholder with the correct value from CMAKE_INSTALL_LIBDIR when generating the final sentry.pc file.
  _{severity: 0.75, confidence: 0.95}

_{Did we get this right? 👍 / 👎 to inform future reviews.}