libprom: add pkg-config support

This will cause a libprom.pc file to be emitted during build, allowing
downstream users to query linker/include flags via pkg-config.

Author: flokli

prom/CMakeLists.txt

@@ -136,6 +136,9 @@ set(CPACK_PACKAGE_DESCRIPTION_FILE ${CMAKE_CURRENT_SOURCE_DIR}/../README.md)
 set(CPACK_PACKAGE_DESCRIPTION_SUMMARY "A prometheus client library")
 set(CPACK_PACKAGE_HOMEPAGE_URL https://github.internal.digitalocean.com/timeseries/prometheus-client-c)
 
+set(target1 libprom)
+configure_file(libprom.pc.in ${CMAKE_INSTALL_LIBDIR}/pkgconfig/libprom.pc @ONLY)
+
 include(CPack)
 include(GNUInstallDirs)
 install(TARGETS prom ARCHIVE)

prom/libprom.pc.in

@@ -0,0 +1,11 @@
+prefix="@CMAKE_INSTALL_PREFIX@"
+exec_prefix="${prefix}"
+libdir="${prefix}/lib"
+includedir="${prefix}/include"
+
+Name: @PROJECT_NAME@
+Description: @CMAKE_PROJECT_DESCRIPTION@
+URL: @CMAKE_PROJECT_HOMEPAGE_URL@
+Version: @PROJECT_VERSION@
+Libs: -L"${libdir}" -l@target1@
+Cflags: -I"${includedir}"