[pushed] Darwin: Fix empty g++ command lines [PR105599].

[pushed] Darwin: Fix empty g++ command lines [PR105599].

[Iain Sandoe]

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.

tested on x86-64-darwin18/19, pushed to master,
thanks
Iain

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.
---
 gcc/config/darwin.h | 17 ++++++-----------
 1 file changed, 6 insertions(+), 11 deletions(-)

diff --git a/gcc/config/darwin.h b/gcc/config/darwin.h
index b73e12372d8..f82ec62cf20 100644
--- a/gcc/config/darwin.h
+++ b/gcc/config/darwin.h
@@ -143,10 +143,7 @@ extern GTY(()) int darwin_ms_struct;
    Right now there's no mechanism to split up the "variable portion" (%*) of
    the matched spec string, so where we have some driver specs that take 2
    or 3 arguments, these cannot be processed here, but are deferred until the
-   LINK_SPEC, where they are copied verbatim.
-   We have a "safe" version of the MacOS version string, that's been sanity-
-   checked and truncated to minor version.  If the 'tiny' (3rd) portion of the
-   value is not significant, it's better to use this in version-compare().  */
+   LINK_SPEC, where they are copied verbatim.  */
 
 #undef SUBTARGET_DRIVER_SELF_SPECS
 #define SUBTARGET_DRIVER_SELF_SPECS					\
@@ -220,13 +217,8 @@ 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 %*; \
-     :%{shared-libgcc: \
-       %:version-compare(< 10.5 asm_macosx_version_min= -Xlinker) \
-       %:version-compare(< 10.5 asm_macosx_version_min= -multiply_defined) \
-       %:version-compare(< 10.5 asm_macosx_version_min= -Xlinker) \
-       %:version-compare(< 10.5 asm_macosx_version_min= suppress)}} \
-     %<multiply_defined*",						\
+  "%{multiply_defined*:-Xlinker -multiply_defined -Xlinker %*} \
+     %<multiply_defined* ",						\
   "%{multiplydefinedunused*:\
      -Xlinker -multiply_defined_unused -Xlinker %*} \
      %<multiplydefinedunused* ",					\
@@ -458,6 +450,9 @@ extern GTY(()) int darwin_ms_struct;
    %{!force_cpusubtype_ALL:-arch %(darwin_subarch)} "\
    LINK_SYSROOT_SPEC \
   "%{mmacosx-version-min=*:-macosx_version_min %*} \
+   %{!multiply_defined*:%{shared-libgcc: \
+     %:version-compare(< 10.5 mmacosx-version-min= -multiply_defined) \
+     %:version-compare(< 10.5 mmacosx-version-min= suppress) }} \
    %{sectalign*} %{sectcreate*} %{sectobjectsymbols*}  %{sectorder*} \
    %{segaddr*} %{segcreate*} %{segprot*} "
 
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