Fix build on Mac with gcc and XCode 11

There is a bug in XCode 11 which makes some standard C headers
not self sufficient when compile with gcc. At least <stdlib.h> and
<algorithm> are affected. When they are included first,
compilation fails with creepy errors like this:

    In file included
    from /Applications/Xcode.app/Contents/Developer/
        Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/
        sys/wait.h:110,
    from /Applications/Xcode.app/Contents/Developer/
        Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/
        stdlib.h:66,
    from tarantool/third_party/zstd/lib/common/zstd_common.c:16:
        /Applications/Xcode.app/Content/Developer/
        Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/
        sys/resource.h:
    In function 'getiopolicy_np': /Applications/Xcode.app/Contents/Developer/
        Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/
        sys/resource.h:447:34: error:
            expected declaration specifiers before '__OSX_AVAILABLE_STARTING'
            447 | int     getiopolicy_np(int, int)
            __OSX_AVAILABLE_STARTING(__MAC_10_5, __IPHONE_2_0);

The patch workarounds the bug by deleting the buggy header
includes where possible, and by changing include order in other
cases.

Also there was a second compilation problem. This was about
different definitions of the same standard functions: via extern
"C" and without. It looked like this:

    In file included from tarantool/src/trivia/util.h:36,
    from tarantool/src/tt_pthread.h:35,
    from tarantool/src/lib/core/fiber.h:38,
    from tarantool/src/lib/core/coio.h:33,
    from tarantool/src/lib/core/coio.cc:31:
    /usr/local/Cellar/gcc/9.2.0_1/lib/gcc/9/gcc/x86_64-apple-darwin18/9.2.0
    include-fixed/stdio.h:222:7: error: conflicting declaration of
    'char* ctermid(char*)' with 'C' linkage
      222 | char *ctermid(char *);
          |       ^~~~~~~

    In file included from /Applications/Xcode.app/Contents/Developer/Platforms/
    MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/unistd.h:525,
    from tarantool/src/lib/core/fiber.h:37,
    from tarantool/src/lib/core/coio.h:33,
    from tarantool/src/lib/core/coio.cc:31:
    /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/
    Developer/SDKs/MacOSX.sdk/usr/include/_ctermid.h:26:10: note: previous
    declaration with 'C++' linkage
      26 | char    *ctermid(char *);
         |          ^~~~~~~

This bug is workarounded by deletion of the conflicting includes,
because anyway they appeared to be not needed.

Closes #4580

Conflicts:
	third_party/decNumber