Install FindPFM.cmake for bencmarkConfig.cmake (google#1942)

There is no upstream PFM cmake package config file to use, so this has
to be installed for the benchmark cmake package config file to work.

Bug: https://bugs.gentoo.org/950573
See-Also: c214639

Signed-off-by: Alfred Wingate <parona@protonmail.com>

Author: parona-source

cmake/Config.cmake.in

@@ -5,6 +5,7 @@ include (CMakeFindDependencyMacro)
 find_dependency (Threads)
 
 if (@BENCHMARK_ENABLE_LIBPFM@)
+    list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_LIST_DIR}")
     find_dependency (PFM)
 endif()
 

src/CMakeLists.txt

@@ -39,6 +39,9 @@ set_property(
 if (PFM_FOUND)
   target_link_libraries(benchmark PRIVATE PFM::libpfm)
   target_compile_definitions(benchmark PRIVATE -DHAVE_LIBPFM)
+  install(
+      FILES "${PROJECT_SOURCE_DIR}/cmake/Modules/FindPFM.cmake"
+      DESTINATION "${CMAKE_INSTALL_LIBDIR}/cmake/${PROJECT_NAME}")
 endif()
 
 # pthread affinity, if available