Fix x86-64 Android build.

runtime/vm/signal_handler_android.cc

Index: runtime/vm/signal_handler_android.cc
diff --git a/runtime/vm/signal_handler_android.cc b/runtime/vm/signal_handler_android.cc
index a85dbb78a4d31dc1f867008bbac8675b36d7d77b..d41eb594ad86fb7b106ad2d0e959032c4c3283ab 100644
--- a/runtime/vm/signal_handler_android.cc
+++ b/runtime/vm/signal_handler_android.cc
@@ -14,6 +14,8 @@ uintptr_t SignalHandler::GetProgramCounter(const mcontext_t& mcontext) {
 
 #if defined(HOST_ARCH_IA32)
   pc = static_cast<uintptr_t>(mcontext.gregs[REG_EIP]);
+#elif defined(HOST_ARCH_X64)
+  pc = static_cast<uintptr_t>(mcontext.gregs[REG_RIP]);
 #elif defined(HOST_ARCH_ARM)
   pc = static_cast<uintptr_t>(mcontext.arm_pc);
 #elif defined(HOST_ARCH_ARM64)
@@ -30,6 +32,8 @@ uintptr_t SignalHandler::GetFramePointer(const mcontext_t& mcontext) {
 
 #if defined(HOST_ARCH_IA32)
   fp = static_cast<uintptr_t>(mcontext.gregs[REG_EBP]);
+#elif defined(HOST_ARCH_X64)
+  fp = static_cast<uintptr_t>(mcontext.gregs[REG_RBP]);
 #elif defined(HOST_ARCH_ARM)
   fp = static_cast<uintptr_t>(mcontext.arm_fp);
 #elif defined(HOST_ARCH_ARM64)
@@ -47,6 +51,8 @@ uintptr_t SignalHandler::GetCStackPointer(const mcontext_t& mcontext) {
 
 #if defined(HOST_ARCH_IA32)
   sp = static_cast<uintptr_t>(mcontext.gregs[REG_ESP]);
+#elif defined(HOST_ARCH_X64)
+  sp = static_cast<uintptr_t>(mcontext.gregs[REG_RSP]);
 #elif defined(HOST_ARCH_ARM)
   sp = static_cast<uintptr_t>(mcontext.arm_sp);
 #elif defined(HOST_ARCH_ARM64)
@@ -63,6 +69,8 @@ uintptr_t SignalHandler::GetDartStackPointer(const mcontext_t& mcontext) {
 
 #if defined(HOST_ARCH_IA32)
   sp = static_cast<uintptr_t>(mcontext.gregs[REG_ESP]);
+#elif defined(HOST_ARCH_X64)
+  sp = static_cast<uintptr_t>(mcontext.gregs[REG_RSP]);
 #elif defined(HOST_ARCH_ARM)
   sp = static_cast<uintptr_t>(mcontext.arm_sp);
 #elif defined(HOST_ARCH_ARM64)
@@ -79,6 +87,8 @@ uintptr_t SignalHandler::GetLinkRegister(const mcontext_t& mcontext) {
 
 #if defined(HOST_ARCH_IA32)
   lr = 0;
+#elif defined(HOST_ARCH_X64)
+  lr = 0;
 #elif defined(HOST_ARCH_ARM)
   lr = static_cast<uintptr_t>(mcontext.arm_lr);
 #elif defined(HOST_ARCH_ARM64)