CMake: folly-deps: gflags is gflags-shared on Fedora #753

Summary:
This targets Fedora specifically. More details are available in #753

I personally do not think this is the best way to handle this, but it's something (and works). Still, there might be a chance for this to get merged in? Thank you!

/cc yfeldblum
Closes https://github.com/facebook/folly/pull/789

Reviewed By: simpkins

Differential Revision: D7111531

Pulled By: yfeldblum

fbshipit-source-id: 508aeeeb7bfaf2402150cd33f7d6c8b726539053

CMake/folly-deps.cmake

@@ -26,7 +26,13 @@ find_package(gflags CONFIG QUIET)
 if (gflags_FOUND)
   message(STATUS "Found gflags from package config")
   set(FOLLY_HAVE_LIBGFLAGS ON)
-  set(FOLLY_SHINY_DEPENDENCIES ${FOLLY_SHINY_DEPENDENCIES} gflags)
+  if (TARGET gflags-shared)
+    set(FOLLY_SHINY_DEPENDENCIES ${FOLLY_SHINY_DEPENDENCIES} gflags-shared)
+  elseif (TARGET gflags)
+    set(FOLLY_SHINY_DEPENDENCIES ${FOLLY_SHINY_DEPENDENCIES} gflags)
+  else()
+    message(FATAL_ERROR "Unable to determine the target name for the GFlags package.")
+  endif()
   list(APPEND CMAKE_REQUIRED_LIBRARIES ${GFLAGS_LIBRARIES})
   list(APPEND CMAKE_REQUIRED_INCLUDES ${GFLAGS_INCLUDE_DIR})
 else()