Hi, this is the 2nd version of the patch.

the main changes are:

    1. some typo.
    2. enhance the error message to provide user idea on how to increase the limit.

bootstrap and regression tested on X86, no issue.

Okay for trunk?

thanks.

Qing

gcc/ChangeLog:

2019-06-03  qing zhao  <qing.zhao@oracle.com>

        * doc/cppopts.texi: Add document for -fmax-include-depth.
        * doc/invoke.texi (Preprocessor Options): List -fmax-include-depth.

libcpp/ChangeLog:

2019-06-03  qing zhao  <qing.zhao@oracle.com>

        * directives.c (do_include_common): Replace CPP_STACK_MAX with
        CPP_OPTION (pfile, max_include_depth).
        * include/cpplib.h (struct cpp_options): Add new field
        max_include_depth.
        * init.c (cpp_create_reader): Initiate new field max_include_depth.
        * internal.h: Delete CPP_STACK_MAX.

gcc/c-family/ChangeLog:

2019-06-03  qing zhao  <qing.zhao@oracle.com>

        * c-opts.c (c_common_handle_option): Handle -fmax-include-depth.
        * c.opt: Add new option -fmax-include-depth.

gcc/testsuite/ChangeLog:

2019-06-03  qing zhao  <qing.zhao@oracle.com>

        * c-c++-common/cpp/fmax-include-depth-1a.h: New test.
        * c-c++-common/cpp/fmax-include-depth-1b.h: New test.
        * c-c++-common/cpp/fmax-include-depth.c: New test.