glr.c: work around ICC limitations

glr.c: work around ICC limitations

The CI is littered with

    #                             -*- compilation -*-
    423. regression.at:907: testing Dancer %glr-parser ...
    ./regression.at:907: bison -fno-caret -o dancer.c dancer.y
    ./regression.at:907: $BISON_C_WORKS
    stderr:
    stdout:
    ./regression.at:907: $CC $CFLAGS $CPPFLAGS  $LDFLAGS -o dancer dancer.c $LIBS
    stderr:
    icc: command line warning #10006: ignoring unknown option '-Wcast-align'
    icc: command line warning #10006: ignoring unknown option '-fparse-all-comments'
    icc: command line warning #10006: ignoring unknown option '-Wdocumentation'
    icc: command line warning #10006: ignoring unknown option '-Wnull-dereference'
    icc: command line warning #10006: ignoring unknown option '-Wbad-function-cast'
    icc: command line warning #10006: ignoring unknown option '-fno-color-diagnostics'
    icc: command line warning #10006: ignoring unknown option '-Wno-keyword-macro'
    dancer.c(755): error #1628: function declared with "noreturn" does return
      }
      ^

    dancer.c(761): error #1628: function declared with "noreturn" does return
      }
      ^

    compilation aborted for dancer.c (code 2)

ICC sees that `longjmp(buf, 1);` does not return, it sees that
`abort();` does not either, but fails to see it for
`longjmp(buf, 1); abort();`

* data/glr.c (YYLONGJMP): Be even clearer on the fact this does not
return.