[PATCH][committed] RISC-V: Add multiarch support on riscv-linux-gnu

[Jeff Law]

This adds multiarch support to the RISC-V port so that bootstraps work 
with Debian out-of-the-box.  Without this patch the stage1 compiler is 
unable to find headers/libraries when building the stage1 runtime.

This is functionally (and possibly textually) equivalent to Debian's fix 
for the same problem.

gcc/
        * config/riscv/t-linux: Add MULTIARCH_DIRNAME.

Pushed to the trunk on Raphael's behalf.

Jeff
commit 47f95bc4be4eb14730ab3eaaaf8f6e71fda47690
Author: Raphael Moreira Zinsly <rzin...@ventanamicro.com>
Date:   Tue Aug 22 11:37:04 2023 -0600

    RISC-V: Add multiarch support on riscv-linux-gnu
    
    This adds multiarch support to the RISC-V port so that bootstraps work with
    Debian out-of-the-box.  Without this patch the stage1 compiler is unable to
    find headers/libraries when building the stage1 runtime.
    
    This is functionally (and possibly textually) equivalent to Debian's fix for
    the same problem.
    
    gcc/
            * config/riscv/t-linux: Add MULTIARCH_DIRNAME.

diff --git a/gcc/config/riscv/t-linux b/gcc/config/riscv/t-linux
index 216d2776a18..a6f64f88d25 100644
--- a/gcc/config/riscv/t-linux
+++ b/gcc/config/riscv/t-linux
@@ -1,3 +1,5 @@
 # Only XLEN and ABI affect Linux multilib dir names, e.g. /lib32/ilp32d/
 MULTILIB_DIRNAMES := $(patsubst rv32%,lib32,$(patsubst 
rv64%,lib64,$(MULTILIB_DIRNAMES)))
 MULTILIB_OSDIRNAMES := $(patsubst lib%,../lib%,$(MULTILIB_DIRNAMES))
+
+MULTIARCH_DIRNAME := $(call if_multiarch,$(firstword $(subst -, 
,$(target)))-linux-gnu)