[Bug target/84260] New: gcc for mips produces an error when called with --help=<class>

["niva at niisi dot msk.ru" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84260

            Bug ID: 84260
           Summary: gcc for mips produces an error when called with
                    --help=<class>
           Product: gcc
           Version: 7.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: niva at niisi dot msk.ru
  Target Milestone: ---

Gcc configured for a mips target:

Target: mips64-niisi_ocrv_posix-elf
Configured with: /home/sap/src/bt23j-gcc-7.3.1/configure
--target=mips64-niisi_ocrv_posix-elf --prefix=/home/sap/local-bt23jj-7.3
--enable-threads=posix --disable-shared --enable-libgomp --enable-libatomic
--enable-lto --enable-languages=c,c++ --program-transform-name='s,^,bt23jj-,'
--disable-tls --enable-serial-configure --disable-__cxa_atexit --with-sysroot
--with-gmp=/home/sap/gcc-infra --with-mpfr=/home/sap/gcc-infra
--with-mpc=/home/sap/gcc-infra
Thread model: posix
gcc version 7.3.0 (GCC) 

produces the following error when called with --help=target (or other class):

cc1: error: position-independent code requires ‘-mabicalls’

The error is issued in mips_option_override because it is called
earlier than finish_options where the proper default value 
global_options.x_flag_pic=0 is set. When mips_option_override is
called, global_options.x_flag_pic==-1.

Probably mips_option_override should check the condition (flag_pic > 0).