[Bug other/105527] New: configure option --with-zstd is not documented

["bruno at clisp dot org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105527

            Bug ID: 105527
           Summary: configure option --with-zstd is not documented
           Product: gcc
           Version: 12.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: other
          Assignee: unassigned at gcc dot gnu.org
          Reporter: bruno at clisp dot org
  Target Milestone: ---

A GCC 12.1.0 build of mine is failing with the error messages

/usr/lib/gcc-cross/i686-linux-gnu/10/../../../../i686-linux-gnu/bin/ld:
/build-loongarch64-linux/gcc-12.1.0/gcc/../../../../sources/gcc-12.1.0/gcc/lto-compress.cc:170:
undefined reference to `ZSTD_isError'
/usr/lib/gcc-cross/i686-linux-gnu/10/../../../../i686-linux-gnu/bin/ld:
/build-loongarch64-linux/gcc-12.1.0/gcc/../../../../sources/gcc-12.1.0/gcc/lto-compress.cc:171:
undefined reference to `ZSTD_getErrorName'
collect2: error: ld returned 1 exit status
make: *** [/sources/gcc-12.1.0/gcc/c/Make-lang.in:87: cc1] error 1

Obviously, the ZStd prerequisite is missing. The documentation (in
gcc-12.1.0/gcc/doc/gccinstall.info and in
https://gcc.gnu.org/install/prerequisites.html) merely says "Alternatively, the
--with-zstd configure option should be used." But what is its argument?

I would expect to see this documented
1. in gcc-12.1.0/gcc/doc/gccinstall.info node "Configuration",
2. also in https://gcc.gnu.org/install/configure.html.

The only hint I can get is by running "gcc-12.1.0/gcc/configure --help", which
prints

  --with-zstd=PATH        specify prefix directory for installed zstd library.
                          Equivalent to --with-zstd-include=PATH/include plus
                          --with-zstd-lib=PATH/lib
  --with-zstd-include=PATH
                          specify directory for installed zstd include files
  --with-zstd-lib=PATH    specify directory for the installed zstd library

This text gives the answer. It should be added to the .texi documentation.