Modernise CMake

* Use `GNUInstallDirs` in order to respect GNU conventions.
  This is especially important for multi-arch/multi-lib setups.
* Specify position independent mode building properly, without
  using the historic hack of adding `-fPIC` as a definition.
  This makes the build system more portable.
* Only detect C++ (and not C) to slightly speed up configuring.
* Specify C++11 mode using modern CMake idioms.
* Fix some whitespace issues.

External/CMakeLists.txt

@@ -2,33 +2,32 @@
 set_property(DIRECTORY APPEND PROPERTY COMPILE_OPTIONS -w)
 
 if (TARGET gmock)
-  message(STATUS "Google Mock already configured - use it")
+    message(STATUS "Google Mock already configured - use it")
 elseif(IS_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}/googletest)
-  # We need to make sure Google Test does not mess up with the
-  # global CRT settings on Windows.
-  if(WIN32)
-    set(gtest_force_shared_crt ON CACHE BOOL "" FORCE)
-  endif(WIN32)
-  add_subdirectory(googletest)
-  set(GTEST_TARGETS
-    gtest
-    gtest_main
-    gmock
-    gmock_main
-  )
-  foreach(target ${GTEST_TARGETS})
-    set_property(TARGET ${target} PROPERTY FOLDER gtest)
-  endforeach()
-  mark_as_advanced(gmock_build_tests
-    BUILD_GMOCK
-    BUILD_GTEST
-    BUILD_SHARED_LIBS
-    gtest_build_samples
-    gtest_build_tests
-    gtest_disable_pthreads
-    gtest_force_shared_crt
-    gtest_hide_internal_symbols)
+    # We need to make sure Google Test does not mess up with the
+    # global CRT settings on Windows.
+    if(WIN32)
+        set(gtest_force_shared_crt ON CACHE BOOL "" FORCE)
+    endif(WIN32)
+    add_subdirectory(googletest)
+    set(GTEST_TARGETS
+        gtest
+        gtest_main
+        gmock
+        gmock_main)
+    foreach(target ${GTEST_TARGETS})
+        set_property(TARGET ${target} PROPERTY FOLDER gtest)
+    endforeach()
+    mark_as_advanced(gmock_build_tests
+        BUILD_GMOCK
+        BUILD_GTEST
+        BUILD_SHARED_LIBS
+        gtest_build_samples
+        gtest_build_tests
+        gtest_disable_pthreads
+        gtest_force_shared_crt
+        gtest_hide_internal_symbols)
 else()
-  message(STATUS
-    "Google Mock was not found - tests based on that will not build")
+    message(STATUS
+        "Google Mock was not found - tests based on that will not build")
 endif()