Only build LLVM for AArch64, ARM, and X86.

Fixes: 141438959
Test: Build toolchain.
Test: Verify LLVM supports fewer targets.
Change-Id: Icb707e52b84cc958ff93ba573207a745e0825443
diff --git a/config_toml.py b/config_toml.py
index 1c13146..e39a2ed 100644
--- a/config_toml.py
+++ b/config_toml.py
@@ -67,6 +67,8 @@
         config_toml.write("""\
 [llvm]
 ninja = true
+targets = "AArch64;ARM;X86"
+experimental-targets = ""
 [build]
 target = {all_targets_config}
 cargo = "{cargo}"