[Bug target/112864] New: [14 regression] Many libphobos tests FAIL on macOS 12+

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112864

            Bug ID: 112864
           Summary: [14 regression] Many libphobos tests FAIL on macOS 12+
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ro at gcc dot gnu.org
                CC: iains at gcc dot gnu.org, ibuclaw at gcc dot gnu.org
  Target Milestone: ---
            Target: x86_64-apple-darwin2[1-3]

Between 20231013 and 20231027, all libphobos tests started to FAIL on macOS
12+:

FAIL: libphobos.aa/test_aa.d (test for excess errors)
Excess errors:
ld: warning: duplicate -rpath
'/private/var/gcc/regression/master/14-gcc/build/x86_64-apple-darwin23.1.0/libphobos/src'
ignored

The duplication can be seen in the log:

Executing on host: /var/gcc/regression/master/14-gcc/build/./gcc/gdc
-B/var/gcc/regression/master/14-gcc/build/./gcc/
-B/vol/gcc/x86_64-apple-darwin23.1.0/bin/
-B/vol/gcc/x86_64-apple-darwin23.1.0/lib/ -isystem
/vol/gcc/x86_64-apple-darwin23.1.0/include -isystem
/vol/gcc/x86_64-apple-darwin23.1.0/sys-include -fchecking=1 -fmessage-length=0
-fno-show-column -Wall -g -O2 -fversion=Shared -fall-instantiations
-fpreview=dip1000 -fno-release -funittest -nostdinc
-B/var/gcc/regression/master/14-gcc/build/x86_64-apple-darwin23.1.0/libphobos/src
-I/var/gcc/regression/master/14-gcc/build/x86_64-apple-darwin23.1.0/libphobos/libdruntime
-I/vol/gcc/src/hg/master/local/libphobos/libdruntime
-I/vol/gcc/src/hg/master/local/libphobos/src 
/vol/gcc/src/hg/master/local/libphobos/testsuite/libphobos.aa/test_aa.d    
-fno-diagnostics-show-caret -fdiagnostics-color=never
-B/var/gcc/regression/master/14-gcc/build/x86_64-apple-darwin23.1.0/libphobos/src
-B/var/gcc/regression/master/14-gcc/build/x86_64-apple-darwin23.1.0/libphobos/libdruntime/gcc
-B/var/gcc/regression/master/14-gcc/build/x86_64-apple-darwin23.1.0/libphobos/src/.libs
-L/var/gcc/regression/master/14-gcc/build/x86_64-apple-darwin23.1.0/libphobos/src/.libs
 -lm  -o ./test_aa.exe    (timeout = 1200)

where there are three instances of -B.../libphobos/src.

PR target/112863 shows a similar issue.