[gcc r13-4870] c++, driver: Fix -static-libstdc++ for targets without Bstatic/dynamic.

[gcc r13-4870] c++, driver: Fix -static-libstdc++ for targets without Bstatic/dynamic.

[Iain D Sandoe]

https://gcc.gnu.org/g:a846817739c1e7b930d593cd51963d6b46b5dfc6

commit r13-4870-ga846817739c1e7b930d593cd51963d6b46b5dfc6
Author: Iain Sandoe <iain@sandoe.co.uk>
Date:   Thu Jan 6 08:37:18 2022 +0000

    c++, driver: Fix -static-libstdc++ for targets without Bstatic/dynamic.
    
    The current implementation for swapping between the static and shared c++
    runtimes relies on the static linker supporting Bstatic/dynamic which is
    not available for every target (Darwin's linker does not support this).
    
    Specs substitution (%s) is an alternative solution for this (which is what
    Darwin uses for Fortran, D and Objective-C).  However, specs substitution
    requires that the '-static-libstdc++' be preserved in the driver's command
    line.  The patch here arranges for this to be done when the configuration
    determines that linker support for Bstatic/dynamic is missing.
    
    Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>
    
    gcc/cp/ChangeLog:
    
            * g++spec.cc (lang_specific_driver): Preserve -static-libstdc++ in
            the driver command line for targets without -Bstatic/dynamic support
            in their static linker.

Diff:
---
 gcc/cp/g++spec.cc | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/gcc/cp/g++spec.cc b/gcc/cp/g++spec.cc
index 3d3b042dd56..f95d7965355 100644
--- a/gcc/cp/g++spec.cc
+++ b/gcc/cp/g++spec.cc
@@ -234,7 +234,12 @@ lang_specific_driver (struct cl_decoded_option **in_decoded_options,
 
 	case OPT_static_libstdc__:
 	  library = library >= 0 ? 2 : library;
+#ifdef HAVE_LD_STATIC_DYNAMIC
+	  /* Remove -static-libstdc++ from the command only if target supports
+	     LD_STATIC_DYNAMIC.  When not supported, it is left in so that a
+	     back-end target can use outfile substitution.  */
 	  args[i] |= SKIPOPT;
+#endif
 	  break;
 
 	case OPT_stdlib_: