[gcc r11-11353] Darwin: Fix empty g++ command lines [PR105599].

[gcc r11-11353] Darwin: Fix empty g++ command lines [PR105599].

[Iain D Sandoe]

https://gcc.gnu.org/g:3bb14f6ed5bc70e25381c67963c90eaab91eca22

commit r11-11353-g3bb14f6ed5bc70e25381c67963c90eaab91eca22
Author: Iain Sandoe <iain@sandoe.co.uk>
Date:   Sun May 29 16:14:32 2022 +0100

    Darwin: Fix empty g++ command lines [PR105599].
    
    An empty g++ command line should produce a diagnostic that there are no
    inputs.  The PR is that currently Darwin produces a dignostic about missing
    link items instead - this is because (errnoeously), for this driver, we are
    creating a link job for empty command lines.
    
    The problem occurs in four stages:
    
     The g++ driver appends -shared-libgcc to the command line.
    
     The Darwin driver_init code in the backend does not see this (it sees an
     empty command line).
    
     When the back end driver code driver sees an empty command line, it does not
     add any supplementary flags (e.g. asm-macosx-version-min) - precisely to
     avoid anything being claimed as an input_file and therefore triggering a link
     line.
    
     Since we do not have a value for asm-macosx-version-min when processing the
     driver specs, we unconditionally inject 'multiply_defined suppress' which is
     used with shared libgcc (but only intended on very old Darwin).  This then
     causes the generation of a link job.
    
    The solution, for the present, is to move version-specific link params to the
    LINK_SPEC so that they are only processed when a link job has already been
    decided.
    
    Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>
    
            PR target/105599
    
    gcc/ChangeLog:
    
            * config/darwin.h: Move versions-specific handling of multiply_defined
            from SUBTARGET_DRIVER_SELF_SPECS to LINK_SPEC.
    
    (cherry picked from commit 794737976b9a6418eab817f143bb4eb2d0c834d2)

Diff:
---
 gcc/config/darwin.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/gcc/config/darwin.h b/gcc/config/darwin.h
index b2bd33f8d4a..5be13293319 100644
--- a/gcc/config/darwin.h
+++ b/gcc/config/darwin.h
@@ -215,7 +215,8 @@ extern GTY(()) int darwin_ms_struct;
   "%{image_base*:-Xlinker -image_base -Xlinker %*} %<image_base*",	\
   "%{init*:-Xlinker -init -Xlinker %*} %<init*",			\
   "%{multi_module:-Xlinker -multi_module} %<multi_module",		\
-  "%{multiply_defined*:-Xlinker -multiply_defined -Xlinker %*} ",	\
+  "%{multiply_defined*:-Xlinker -multiply_defined -Xlinker %*} \
+     %<multiply_defined* ",						\
   "%{multiplydefinedunused*:\
      -Xlinker -multiply_defined_unused -Xlinker %*} \
      %<multiplydefinedunused* ",					\