Fix build.

runtime/bin/main.cc

Index: runtime/bin/main.cc
diff --git a/runtime/bin/main.cc b/runtime/bin/main.cc
index 1e3d8479388a0adc590117e74ac35d70d6f54bdb..4126cbcdda96ae49f7d519f72bba4d257b342205 100644
--- a/runtime/bin/main.cc
+++ b/runtime/bin/main.cc
@@ -1445,6 +1445,7 @@ static void GeneratePrecompiledSnapshot() {
 }
 
 
+#if defined(TARGET_ARCH_X64)
 static void GeneratePrecompiledJITSnapshot() {
   uint8_t* vm_isolate_buffer = NULL;
   intptr_t vm_isolate_size = 0;
@@ -1476,6 +1477,7 @@ static void GeneratePrecompiledJITSnapshot() {
                    rodata_blob_buffer,
                    rodata_blob_size);
 }
+#endif  // defined(TARGET_ARCH_X64)
 
 
 static void GenerateAppSnapshot() {