libgcc9 broken symbolic link libgcc_ext.10.5.dylib and libgcc_ext.10.4.dylib

[Serge3leo (Serguei E. Leontiev)]

Clean install gcc9 (macOS Catalina 10.15.7 (19H1824), Xcode 12.4 (12D4e))

$ ls -lL `port contents gcc9 | sed -e 1d` > /dev/null
ls: libgcc_ext.10.4.dylib: No such file or directory
ls: libgcc_ext.10.5.dylib: No such file or directory
$ LANG=C ls -lL /opt/local/lib/gcc9/libgcc_ext.10.*
lrwxr-xr-x  1 root  admin  43 Dec 26 00:47 /opt/local/lib/gcc9/libgcc_ext.10.4.dylib -> /opt/local/lib/libgcc/libgcc_ext.10.4.dylib
lrwxr-xr-x  1 root  admin  43 Dec 26 00:47 /opt/local/lib/gcc9/libgcc_ext.10.5.dylib -> /opt/local/lib/libgcc/libgcc_ext.10.5.dylib
ls: libgcc_ext.10.4.dylib: No such file or directory
ls: libgcc_ext.10.5.dylib: No such file or directory

$ port installed requested
The following ports are currently installed:
  gcc9 @9.4.0_1 (active)

$ port installed
The following ports are currently installed:
  cctools @949.0.1_2+xcode (active)
  gcc9 @9.4.0_1 (active)
  gcc_select @0.1_9 (active)
  gettext-runtime @0.21_0 (active)
  gmp @6.2.1_1 (active)
  isl @0.24_1 (active)
  ld64 @3_4+ld64_xcode (active)
  ld64-xcode @2_4 (active)
  libgcc @5.0_0 (active)
  libgcc9 @9.4.0_0 (active)
  libgcc10 @10.3.0_3 (active)
  libgcc11 @11.3.0_0 (active)
  libiconv @1.16_1 (active)
  libmpc @1.2.1_0 (active)
  mpfr @4.1.0_0 (active)
  xz @5.2.5_1 (active)
  zlib @1.2.12_0 (active)

Build failed of simple program:

$ gfortran-mp-9 ref-hello_world.f
ld: library not found for -lgcc_ext.10.5
collect2: error: ld returned 1 exit status

[Serge3leo (Serguei E. Leontiev)]

Workaround:

$ sudo port build gcc9
...
$ sudo cp /opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_macports_release_tarballs_ports_lang_gcc9/gcc9/work/build/x86_64-apple-darwin19/libgcc/libgcc_ext.10.[45].dylib /opt/local/lib/libgcc/.