Add component CMakeLists.txt file for use with CMake-based build system (#1508)

Includes verification script (for Travis) that CMakeLists.txt contents match
repo & submodule source files

tools/check_cmakelists.sh

@@ -0,0 +1,26 @@
+#!/bin/bash
+#
+# This script is for Travis. It checks all non-examples source files in libraries/ and cores/ are listed in
+# CMakeLists.txt for the cmake-based IDF component
+#
+# If you see an error running this script, edit CMakeLists.txt and add any new source files into your PR
+#
+
+set -e
+
+cd "`dirname $0`/.."  # cd to arduino-esp32 root
+
+# find all source files in repo
+REPO_SRCS=`find cores/esp32/ libraries/ -name 'examples' -prune -o -name 'main.cpp' -prune -o -name '*.c' -print -o -name '*.cpp' -print | sort`
+
+# find all source files named in CMakeLists.txt COMPONENT_SRCS
+CMAKE_SRCS=`cmake --trace-expand -C CMakeLists.txt 2>&1 | grep COMPONENT_SRCS | sed 's/.\+COMPONENT_SRCS //' | sed 's/ )//' | tr ' ;' '\n' | sort`
+
+if ! diff -u0 --label "Repo Files" --label "COMPONENT_SRCS" <(echo "$REPO_SRCS") <(echo "$CMAKE_SRCS"); then
+    echo "Source files in repo (-) and source files in CMakeLists.txt (+) don't match"
+    echo "Edit CMakeLists.txt as appropriate to add/remove source files from COMPONENT_SRCS"
+    exit 1
+fi
+
+echo "CMakeLists.txt and repo source files match"
+exit 0