[vm] Don't generate gen_snapshot targeting ARM/RISCV64 for ARM64C/X64C.

Currently, DART_COMPRESSED_POINTERS is used both for the host and
the target, and the ARM assembler treats it being defined as an
error and the RISCV assembler does not appropriately define certain
methods when compressed pointers are used.

TEST=manual build of create_sdk for arm64c/x64c, since there are no
     pkg/sdk trybots for compressed architectures.

Issue: #28617
Change-Id: Iac31b23b59c0d5cfe2bef007c553f56e5144d782
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/438500
Commit-Queue: Tess Strickland <[email protected]>
Reviewed-by: Martin Kustermann <[email protected]>
Reviewed-by: Ivan Inozemtsev <[email protected]>

Author: sstrickl

sdk/BUILD.gn

@@ -880,13 +880,18 @@ group("create_full_sdk") {
     # SDK, but add them as a dependency, so that they are built.
     public_deps += [
       "../runtime/bin:gen_snapshot_product_linux_arm64",
-      "../runtime/bin:gen_snapshot_product_linux_riscv64",
       "../runtime/bin:gen_snapshot_product_linux_x64",
     ]
 
-    # assembler_arm.cc disallows ARM cross-compilation on Windows.
-    if (!is_win) {
-      public_deps += [ "../runtime/bin:gen_snapshot_product_linux_arm" ]
+    # Don't add cross compilers for architectures that do not support
+    # compressed pointers in SDKs built for compressed pointers.
+    if (!dart_use_compressed_pointers) {
+      public_deps += [ "../runtime/bin:gen_snapshot_product_linux_riscv64" ]
+
+      # assembler_arm.cc disallows ARM cross-compilation on Windows.
+      if (!is_win) {
+        public_deps += [ "../runtime/bin:gen_snapshot_product_linux_arm" ]
+      }
     }
   }
 }