Create Zephyr external module

This update googletest to use it as Zephyr OS external module.
This allows downloading, configure and building googltest using
Zephyr west build system, without any user manipulation.

Signed-off-by: Alexandre Bailon <abailon@baylibre.com>

modules/googletest/CMakeLists.txt

@@ -0,0 +1,17 @@
+zephyr_library()
+
+# Disable use of pthreads in GoogleTest
+set(gtest_disable_pthreads ON CACHE BOOL "Build GoogleTest without Pthread")
+
+zephyr_include_directories_ifdef(CONFIG_GTEST ${ZEPHYR_GOOGLETEST_MODULE_DIR}/googletest/)
+zephyr_include_directories_ifdef(CONFIG_GTEST ${ZEPHYR_GOOGLETEST_MODULE_DIR}/googletest/include/)
+zephyr_library_sources_ifdef(CONFIG_GTEST
+    ${ZEPHYR_GOOGLETEST_MODULE_DIR}/googletest/src/gtest-all.cc
+)
+target_sources_ifdef(CONFIG_GTEST app PRIVATE
+    ${ZEPHYR_GOOGLETEST_MODULE_DIR}/googletest/src/gtest_main.cc
+)
+
+zephyr_include_directories_ifdef(CONFIG_GMOCK ${ZEPHYR_GOOGLETEST_MODULE_DIR}/googlemock/)
+zephyr_include_directories_ifdef(CONFIG_GMOCK ${ZEPHYR_GOOGLETEST_MODULE_DIR}/googlemock/include/)
+zephyr_library_sources_ifdef(CONFIG_GMOCK ${ZEPHYR_GOOGLETEST_MODULE_DIR}/googlemock/src/gmock-all.cc)

modules/googletest/Kconfig

@@ -0,0 +1,18 @@
+config GTEST
+    bool "GoogleTest test framework"
+    select TEST
+    select CPP
+    select REQUIRES_FULL_LIBCPP
+    select FPU
+
+config GMOCK
+    bool "GoogleMock mocking framework"
+    select GTEST
+
+choice STD_CPP
+	default STD_CPP14 if GTEST
+endchoice
+
+choice LIBC_IMPLEMENTATION
+	default NEWLIB_LIBC if GTEST
+endchoice

modules/modules.cmake

@@ -0,0 +1,2 @@
+set(ZEPHYR_GOOGLETEST_CMAKE_DIR ${CMAKE_CURRENT_LIST_DIR}/googletest)
+set(ZEPHYR_GOOGLETEST_KCONFIG   ${CMAKE_CURRENT_LIST_DIR}/googletest/Kconfig)

zephyr/module.yml

@@ -0,0 +1,6 @@
+name: googletest
+build:
+  cmake-ext: true
+  kconfig-ext: true
+  settings:
+    module_ext_root: .