cmake: fix issues in the FindGMock module

Summary:
- Fix the variable name passed to FIND_PACKAGE_HANDLE_STANDARD_ARGS() so that
  it matches the module name (`FindGMock.cmake`).  This makes sure that the
  failure is detected correctly if GMock is not found.
- googletest depends on pthreads, so use `find_package(Threads)` and add
  `Threads::Threads` to the list of required library dependencies.

Reviewed By: yfeldblum

Differential Revision: D9212536

fbshipit-source-id: eae6220a2dbfe777bff1ac0ee0fb4df53de16955

CMake/FindGMock.cmake

@@ -20,6 +20,7 @@ FIND_LIBRARY(LIBGMOCK_LIBRARY_RELEASE NAMES gmock)
 FIND_LIBRARY(LIBGTEST_LIBRARY_DEBUG NAMES gtestd)
 FIND_LIBRARY(LIBGTEST_LIBRARY_RELEASE NAMES gtest)
 
+find_package(Threads REQUIRED)
 INCLUDE(SelectLibraryConfigurations)
 SELECT_LIBRARY_CONFIGURATIONS(LIBGMOCK_MAIN)
 SELECT_LIBRARY_CONFIGURATIONS(LIBGMOCK)
@@ -29,6 +30,7 @@ set(LIBGMOCK_LIBRARIES
   ${LIBGMOCK_MAIN_LIBRARY}
   ${LIBGMOCK_LIBRARY}
   ${LIBGTEST_LIBRARY}
+  Threads::Threads
 )
 
 if(CMAKE_SYSTEM_NAME STREQUAL "Windows")
@@ -44,7 +46,7 @@ endif()
 # all listed variables are TRUE
 INCLUDE(FindPackageHandleStandardArgs)
 FIND_PACKAGE_HANDLE_STANDARD_ARGS(
-  LIBGMOCK
+  GMock
   DEFAULT_MSG
   LIBGMOCK_MAIN_LIBRARY
   LIBGMOCK_LIBRARY