Add riscv64 support for base gn build am: f65f3c34c1

Original change: https://android-review.googlesource.com/c/platform/external/libchrome/+/2263700

Change-Id: Ib8463d5bc27b6f1043a1b995eea8b4d8f2094431
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>
diff --git a/base/process/launch_posix.cc b/base/process/launch_posix.cc
index ec58488..3fcb0b4 100644
--- a/base/process/launch_posix.cc
+++ b/base/process/launch_posix.cc
@@ -728,7 +728,8 @@
   alignas(16) char stack_buf[PTHREAD_STACK_MIN];
 #if defined(ARCH_CPU_X86_FAMILY) || defined(ARCH_CPU_ARM_FAMILY) ||   \
     defined(ARCH_CPU_MIPS_FAMILY) || defined(ARCH_CPU_S390_FAMILY) || \
-    defined(ARCH_CPU_PPC64_FAMILY)
+    defined(ARCH_CPU_PPC64_FAMILY) || defined(ARCH_CPU_LOONG_FAMILY) || \
+    defined(ARCH_CPU_RISCV_FAMILY)
   // The stack grows downward.
   void* stack = stack_buf + sizeof(stack_buf);
 #else