[gcc r14-6219] Modula-2: Support '-isysroot [...]'

[Thomas Schwinge <tschwinge@gcc.gnu.org>]

https://gcc.gnu.org/g:fbacdeff9799f2915e3529d0266006f251ea8344

commit r14-6219-gfbacdeff9799f2915e3529d0266006f251ea8344
Author: Thomas Schwinge <thomas@codesourcery.com>
Date:   Tue Dec 5 09:54:54 2023 +0100

    Modula-2: Support '-isysroot [...]'
    
    In GCC cross configurations (tested '--target=amdgcn-amdhsa' and
    '--target=nvptx-none') with a sysroot configured, the 'gm2' driver invocations
    are passed '--sysroot=[...]', which is translated into '-isysroot [...]' for
    the 'cc1gm2' compiler invocation.  The latter, however gets complained about:
    
        cc1gm2: warning: command-line option ‘-isysroot [...]’ is valid for C/C++/D/Fortran/ObjC/ObjC++ but not for Modula-2
    
    ..., and therefore a ton of FAILs.
    
    Reproducer (also for non-cross, native configurations):
    
        $ build-gcc/gcc/gm2 -Bbuild-gcc/gcc -v --sysroot=/tmp -x modula-2 /dev/null
        [...]
         build-gcc/gcc/cc1gm2 [...] -isysroot [...]/tmp [...]
        cc1gm2: warning: command-line option ‘-isysroot /tmp’ is valid for C/C++/D/Fortran/ObjC/ObjC++ but not for Modula-2
        [...]
    
            gcc/m2/
            * lang.opt (-isysroot): New.

Diff:
---
 gcc/m2/lang.opt | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/gcc/m2/lang.opt b/gcc/m2/lang.opt
index 24f3c6594b9..a60c03e69d4 100644
--- a/gcc/m2/lang.opt
+++ b/gcc/m2/lang.opt
@@ -405,6 +405,10 @@ iquote
 Modula-2
 ; Documented in c.opt
 
+isysroot
+Modula-2
+; Documented in c.opt
+
 isystem
 Modula-2
 ; Documented in c.opt