gcc@10: fix build on arm64 linux

Closes #119825.

Signed-off-by: Patrick Linnane <patrick@linnane.io>
Signed-off-by: BrewTestBot <1589480+BrewTestBot@users.noreply.github.com>

Formula/gcc@10.rb

@@ -23,7 +23,6 @@ class GccAT10 < Formula
   # out of the box on Xcode-only systems due to an incorrect sysroot.
   pour_bottle? only_if: :clt_installed
 
-  depends_on arch: :x86_64
   depends_on "gmp"
   depends_on "isl"
   depends_on "libmpc"
@@ -31,6 +30,10 @@ class GccAT10 < Formula
 
   uses_from_macos "zlib"
 
+  on_macos do
+    depends_on arch: :x86_64
+  end
+
   on_linux do
     depends_on "binutils"
   end
@@ -103,8 +106,12 @@ class GccAT10 < Formula
 
       # Change the default directory name for 64-bit libraries to `lib`
       # https://www.linuxfromscratch.org/lfs/view/development/chapter06/gcc-pass2.html
+      if Hardware::CPU.arm?
+        inreplace "gcc/config/aarch64/t-aarch64-linux", "lp64=../lib64", "lp64="
+      else
         inreplace "gcc/config/i386/t-linux64", "m64=../lib64", "m64="
       end
+    end
 
     mkdir "build" do
       system "../configure", *args