Check if librt exists independent of OS, to be able to exclude librt on Android…

Check if librt exists independent of OS, to be able to exclude librt on Android builds, even though it is a 'Linux'.

CMakeLists.txt

@@ -17,6 +17,8 @@ CMAKE_MINIMUM_REQUIRED(VERSION 2.6)
 # Add find modules to the path
 SET(CMAKE_MODULE_PATH ${CMAKE_MODULE_PATH} "${CMAKE_CURRENT_LIST_DIR}/cmake/Modules/")
 
+INCLUDE(CheckLibraryExists)
+
 # Build options
 #
 OPTION( SONAME				"Set the (SO)VERSION of the target"		ON  )
@@ -78,7 +80,9 @@ FUNCTION(TARGET_OS_LIBRARIES target)
 	ELSEIF(CMAKE_SYSTEM_NAME MATCHES "(Solaris|SunOS)")
 		TARGET_LINK_LIBRARIES(${target} socket nsl)
 		SET(LIBGIT2_PC_LIBS "${LIBGIT2_PC_LIBS} -lsocket -lnsl" PARENT_SCOPE)
-	ELSEIF(CMAKE_SYSTEM_NAME MATCHES "Linux")
+	ENDIF()
+	CHECK_LIBRARY_EXISTS(rt clock_gettime "time.h" NEED_LIBRT)
+	IF(NEED_LIBRT)
 		TARGET_LINK_LIBRARIES(${target} rt)
 		SET(LIBGIT2_PC_LIBS "${LIBGIT2_PC_LIBS} -lrt" PARENT_SCOPE)
 	ENDIF()