Find gtest from devel/gtest.

Index: cmake/modules/FindGTest.cmake
--- cmake/modules/FindGTest.cmake.orig
+++ cmake/modules/FindGTest.cmake
@@ -55,14 +55,30 @@ find_path(GTEST_SOURCE_DIR
 )
 mark_as_advanced(GTEST_SOURCE_DIR)
 
+find_path(GTEST_INCLUDE_DIR
+    NAMES gtest/gtest.h
+    HINTS $ENV{GTEST_ROOT}/include ${GTEST_ROOT}/include
+)
+mark_as_advanced(GTEST_INCLUDE_DIR)
+
+MACRO(GTEST_FIND varname shortname)
+    FIND_LIBRARY(${varname}
+        NAMES ${shortname}
+        PATHS
+        /usr/local/lib
+            NO_DEFAULT_PATH
+        DOC "Location of GTEST Libraries"
+    )
+ENDMACRO(GTEST_FIND)
+
 include(FindPackageHandleStandardArgs)
-find_package_handle_standard_args(GTest DEFAULT_MSG GTEST_SOURCE_DIR)
+find_package_handle_standard_args(GTest DEFAULT_MSG GTEST_INCLUDE_DIR)
 
 if(GTEST_FOUND)
     SET(GTEST_INCLUDE_DIRS
-        ${GTEST_SOURCE_DIR}/include
+        ${GTEST_INCLUDE_DIR}
     )
-    SET(GTEST_SOURCES
-        ${GTEST_SOURCE_DIR}/src/gtest-all.cc
-    )
+    GTEST_FIND(GTEST_LIBRARIES gtest)
+    GTEST_FIND(GTEST_MAIN_LIBRARIES gtest_main)
+    SET(GTEST_BOTH_LIBRARIES ${GTEST_LIBRARIES} ${GTEST_MAIN_LIBRARIES})
 endif()