Add flatbuffer_cc library support (#5061)

* Add flatbuffer_cc library support

* Update flags so all the tests pass

Tests now all pass!

* Modify the tests to use the generated code

This should be a simple serialize/deserialize test of the new generated
code to make sure the bazel rules are doing something sane.

* Use generated monster_test.fb in testing/test.cpp

cmake drops it's generated code in tests/monster_test_generated.h
Instead of checking that in, let's generate it with bazel.

* Make grpc tests depend on monster_test_generated.h

* Remove redundant cmake dependency

This should address @aardappel's feedback.

* Run flatc for Android as well

This will fix the last travis.ci failure

* Add generated output folder and fix flags

* Move flatbuffers_header_build_rules to the library that uses it

* Use --cpp-ptr-type to fix android

Android was the only target using the STL emulation layer.  It needed
the --cpp-ptr-type flatbuffers::unique_ptr flag to work.  Add it!

* Roll back changes to use autogenerated monster_test_generated.

Flip tests/test.cpp to use the autogenerated file as well.

BUILD

@@ -12,6 +12,8 @@ exports_files([
     "LICENSE",
 ])
 
+load(":build_defs.bzl", "flatbuffer_cc_library")
+
 # Public flatc library to compile flatbuffer files at runtime.
 cc_library(
     name = "flatbuffers",
@@ -88,8 +90,8 @@ cc_binary(
         "src/idl_gen_grpc.cpp",
         "src/idl_gen_js_ts.cpp",
         "src/idl_gen_json_schema.cpp",
-        "src/idl_gen_lua.cpp",
         "src/idl_gen_lobster.cpp",
+        "src/idl_gen_lua.cpp",
         "src/idl_gen_php.cpp",
         "src/idl_gen_python.cpp",
         "src/idl_gen_rust.cpp",
@@ -109,6 +111,7 @@ cc_library(
     hdrs = [
         "include/flatbuffers/base.h",
         "include/flatbuffers/flatbuffers.h",
+        "include/flatbuffers/flexbuffers.h",
         "include/flatbuffers/stl_emulation.h",
         "include/flatbuffers/util.h",
     ],
@@ -130,14 +133,14 @@ cc_test(
         "src/idl_parser.cpp",
         "src/reflection.cpp",
         "src/util.cpp",
-        "tests/monster_test_generated.h",
+        "monster_test_generated.h",
         "tests/namespace_test/namespace_test1_generated.h",
         "tests/namespace_test/namespace_test2_generated.h",
         "tests/test.cpp",
-        "tests/test_builder.h",
+        "tests/test_assert.cpp",
         "tests/test_assert.h",
         "tests/test_builder.cpp",
-        "tests/test_assert.cpp",
+        "tests/test_builder.h",
         "tests/union_vector/union_vector_generated.h",
         ":public_headers",
     ],
@@ -155,8 +158,20 @@ cc_test(
         ":tests/prototest/test.golden",
         ":tests/prototest/test.proto",
         ":tests/prototest/test_union.golden",
-        ":tests/union_vector/union_vector.fbs",
         ":tests/unicode_test.json",
+        ":tests/union_vector/union_vector.fbs",
     ],
     includes = ["include/"],
 )
+
+# Test bzl rules
+
+flatbuffer_cc_library(
+    name = "monster_test_cc_fbs",
+    srcs = ["tests/monster_test.fbs"],
+    include_paths = ["tests/include_test"],
+    includes = [
+        "tests/include_test/include_test1.fbs",
+        "tests/include_test/sub/include_test2.fbs",
+    ],
+)