add required symbols

Author: nikomatsakis

src/rt/arch/x86_64/ccall.S

@@ -6,10 +6,18 @@
 // slower.
 #if defined(__APPLE__) || defined(_WIN32)
 .globl _upcall_call_c_stack
+.globl _upcall_call_c_stack_i64
+.globl _upcall_call_c_stack_float
 _upcall_call_c_stack:
+_upcall_call_c_stack_i64:
+_upcall_call_c_stack_float:
 #else
 .globl upcall_call_c_stack
+.globl upcall_call_c_stack_i64
+.globl upcall_call_c_stack_float
 upcall_call_c_stack:
+upcall_call_c_stack_i64:
+upcall_call_c_stack_float:
 #endif
     push %rbp
     mov %rsp,%rbp          // save rsp