[compiler-rt][RISCV] Use u64 data type for marchid and mimpid (llvm#1…

…12163)

Base on riscv-non-isa/riscv-c-api-doc#91 , the
marchid and mimpid are MXLEN bits wide, and kernel returned them as u64
data type. So we should use u64 data type for marchid and mimpid in
__riscv_cpu_model struct here.

Signed-off-by: Yangyu Chen <cyy@cyyself.name>

compiler-rt/lib/builtins/cpu_model/riscv.c

@@ -22,8 +22,8 @@ struct {
 
 struct {
   unsigned mvendorid;
-  unsigned marchid;
-  unsigned mimpid;
+  unsigned long long marchid;
+  unsigned long long mimpid;
 } __riscv_cpu_model __attribute__((visibility("hidden"), nocommon));
 
 // NOTE: Should sync-up with RISCVFeatures.td