* Adds XOPEN_SOURCE for PATH_MAX and POSIX 1993 for stat

These are the only two required extension for compilation of
flatbuffers using -std=c++11 instead of gnu++11.

* Sets _XOPEN_SOURCE to 600 and enable POSIX2001 for fseeko

- Fix GenerateTextFromTable (aliasing typo)
- Fix unused variable in idl_gen_dart.cpp
- Fix std::string passing (should be non-const value or const-reference)
- Remove unused variables

* Set default CRTReportMode for the `flatc` target

* Add util.cpp to GRPC test target

* Fix path to util.h

* Make the Parser independent from the global C-locale

* Set a specific test locale using the environment variable FLATBUFFERS_TEST_LOCALE

* Remove redundant static qualifiers

* The asserts replaced by FLATBUFFERS_ASSERT. Several asserts have converted to static_asserts.

* Regenerate header monster generate_code.sh

Also added missing generated files.

Change-Id: Ifd22a643a08e3f2edfce92812ed57b87fc0e1875

Change-Id: I737f6fd0bb1302ab7cfa6ab8b06108e221ebb63c
Tested: on Linux.

to allow for custom file loaders. The targeted use case is android runtime.

(from CL 116980408)

Change-Id: I8785c0acf714fab41d8f6fc9f1c52875423b8f5b