cmake/modules/BuildRocksDB.cmake: inherit parent's CMAKE_CXX_FLAGS

CMake allows us to customize `CMAKE_CXX_FLAGS` by setting CXXFLAGS
environmental variable. and Debian's debhelper also sets CXXFLAGS
when it builds cmake projects for customizing the building flags.

but we fail to populate this setting down when building external
projects. this is important when it comes to the projects which
is critical to the performance. RocksDB is one of them.

in this change, we pass the `CMAKE_CXX_FLAGS` down in
`BuildRocksDB.cmake` so that its `CMAKE_CXX_FLAGS` contains
the same set of `CMAKE_CXX_FLAGS` used by its parent project.

this should help with the performance in the bluestore, where
RocksDB is used.

Signed-off-by: Kefu Chai <tchaikov@gmail.com>
(cherry picked from commit beb1a624921d7589db63dea066935b3aa9ce2698)

diff --git a/cmake/modules/BuildRocksDB.cmake b/cmake/modules/BuildRocksDB.cmake
index 01b4ef0e31c85bdd71c45ed7af772df54c2a6702..32f8df97619ab3927e5b282ee55e1003e4e9db10 100644 (file)
--- a/cmake/modules/BuildRocksDB.cmake
+++ b/cmake/modules/BuildRocksDB.cmake
@@ -56,6 +56,7 @@ function(build_rocksdb)
   endif()
   include(CheckCXXCompilerFlag)
   check_cxx_compiler_flag("-Wno-deprecated-copy" HAS_WARNING_DEPRECATED_COPY)
+  set(rocksdb_CXX_FLAGS "${CMAKE_CXX_FLAGS}")
   if(HAS_WARNING_DEPRECATED_COPY)
     string(APPEND rocksdb_CXX_FLAGS " -Wno-deprecated-copy")
   endif()