gcc-11 and cmake related cleanup (facebook#9286)

Summary:
in hope to get rockdb compiled with GCC-11 without warning

* util/bloom_test: init a variable before using it
  to silence the GCC warning like
  ```
  util/bloom_test.cc:1253:31: error: ‘<anonymous>’ may be used uninitialized [-Werror=maybe-uninitialized]
   1253 |   Slice key_slice{key_bytes, 8};
        |                               ^
  ...
  include/rocksdb/slice.h:41:3: note: by argument 2 of type ‘const char*’ to ‘rocksdb::Slice::Slice(const char*, size_t)’ declared here
     41 |   Slice(const char* d, size_t n) : data_(d), size_(n) {}
        |   ^~~~~
  util/bloom_test.cc:1249:3: note: ‘<anonymous>’ declared here
   1249 |   };
        |   ^
  cc1plus: all warnings being treated as errors
  ```
* cmake: add find_package(uring ...)
  find liburing in a more consistent way. also it is the encouraged way for finding a library.

Pull Request resolved: facebook#9286

Reviewed By: mrambacher

Differential Revision: D33165241

Pulled By: jay-zhuang

fbshipit-source-id: 9f3487e11b4e40fd8f1c97c8facb24a190e5ce31

Author: tchaikov

CMakeLists.txt

@@ -352,25 +352,17 @@ int main() {
   return 0;
 }
 " BUILTIN_ATOMIC)
-if (NOT BUILTIN_ATOMIC)
-  #TODO: Check if -latomic exists
-  list(APPEND THIRDPARTY_LIBS atomic)
-endif()
+  if (NOT BUILTIN_ATOMIC)
+    #TODO: Check if -latomic exists
+    list(APPEND THIRDPARTY_LIBS atomic)
+  endif()
 endif()
 
 if (WITH_LIBURING)
-  set(CMAKE_REQUIRED_FLAGS "-luring")
-  CHECK_CXX_SOURCE_COMPILES("
-#include <liburing.h>
-int main() {
-  struct io_uring ring;
-  io_uring_queue_init(1, &ring, 0);
-  return 0;
-}
-" HAS_LIBURING)
-  if (HAS_LIBURING)
+  find_package(uring)
+  if (uring_FOUND)
     add_definitions(-DROCKSDB_IOURING_PRESENT)
-    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -luring")
+    list(APPEND THIRDPARTY_LIBS uring::uring)
   endif()
 endif()
 

cmake/modules/Finduring.cmake

@@ -0,0 +1,26 @@
+# - Find liburing
+#
+# uring_INCLUDE_DIR - Where to find liburing.h
+# uring_LIBRARIES - List of libraries when using uring.
+# uring_FOUND - True if uring found.
+
+find_path(uring_INCLUDE_DIR
+  NAMES liburing.h)
+find_library(uring_LIBRARIES
+  NAMES liburing.a liburing)
+
+include(FindPackageHandleStandardArgs)
+find_package_handle_standard_args(uring
+  DEFAULT_MSG uring_LIBRARIES uring_INCLUDE_DIR)
+
+mark_as_advanced(
+  uring_INCLUDE_DIR
+  uring_LIBRARIES)
+
+if(uring_FOUND AND NOT TARGET uring::uring)
+  add_library(uring::uring UNKNOWN IMPORTED)
+  set_target_properties(uring::uring PROPERTIES
+    INTERFACE_INCLUDE_DIRECTORIES "${uring_INCLUDE_DIR}"
+    IMPORTED_LINK_INTERFACE_LANGUAGES "C"
+    IMPORTED_LOCATION "${uring_LIBRARIES}")
+endif()

util/bloom_test.cc

@@ -1244,7 +1244,7 @@ INSTANTIATE_TEST_CASE_P(Full, FullBloomTest,
 
 static double GetEffectiveBitsPerKey(FilterBitsBuilder* builder) {
   union {
-    uint64_t key_value;
+    uint64_t key_value = 0;
     char key_bytes[8];
   };