[RISCV] Fix some GlobalISel tests using -march instead of -mtriple.

This caused llc to assume the wrong target triple and broke some internal
AS sanitizer bots.

Author: aemerson

llvm/test/CodeGen/RISCV/GlobalISel/instruction-select/icmp-rv32.mir

@@ -1,5 +1,5 @@
 # NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
-# RUN: llc -march=riscv32 -run-pass=instruction-select -simplify-mir \
+# RUN: llc -mtriple=riscv32 -run-pass=instruction-select -simplify-mir \
 # RUN: -verify-machineinstrs %s -o - | FileCheck %s
 ---
 name:            cmp_ult_i32

llvm/test/CodeGen/RISCV/GlobalISel/instruction-select/icmp-rv64.mir

@@ -1,5 +1,5 @@
 # NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
-# RUN: llc -march=riscv64 -run-pass=instruction-select -simplify-mir \
+# RUN: llc -mtriple=riscv64 -run-pass=instruction-select -simplify-mir \
 # RUN: -verify-machineinstrs %s -o - | FileCheck %s
 ---
 name:            cmp_ult_i64

llvm/test/CodeGen/RISCV/GlobalISel/instruction-select/ptradd-rv32.mir

@@ -1,5 +1,5 @@
 # NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
-# RUN: llc -march=riscv32 -run-pass=instruction-select -simplify-mir \
+# RUN: llc -mtriple=riscv32 -run-pass=instruction-select -simplify-mir \
 # RUN: -verify-machineinstrs %s -o - | FileCheck %s
 ---
 name:            add_i32

llvm/test/CodeGen/RISCV/GlobalISel/instruction-select/ptradd-rv64.mir

@@ -1,5 +1,5 @@
 # NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
-# RUN: llc -march=riscv64 -run-pass=instruction-select -simplify-mir \
+# RUN: llc -mtriple=riscv64 -run-pass=instruction-select -simplify-mir \
 # RUN: -verify-machineinstrs %s -o - | FileCheck %s
 ---
 name:            add_i64