[RISCV] Add -mtune support

 - The goal of this patch is improve option compatible with RISCV-V GCC,
   -mcpu support on GCC side will sent patch in next few days.

 - -mtune only affect the pipeline model and non-arch/extension related
   target feature, e.g. instruction fusion; in td file it called
   TuneFeatures, which is introduced by X86 back-end[1].

 - -mtune accept all valid option for -mcpu and extra alias processor
   option, e.g. `generic`, `rocket` and `sifive-7-series`, the purpose is
   option compatible with RISCV-V GCC.

 - Processor alias for -mtune will resolve according the current target arch,
   rv32 or rv64, e.g. `rocket` will resolve to `rocket-rv32` or `rocket-rv64`.

 - Interaction between -mcpu and -mtune:
   * -mtune has higher priority than -mcpu for pipeline model and
     TuneFeatures.

[1] https://reviews.llvm.org/D85165

Reviewed By: luismarques

Differential Revision: https://reviews.llvm.org/D89025
diff --git a/clang/test/Misc/target-invalid-cpu-note.c b/clang/test/Misc/target-invalid-cpu-note.c
index c35e6c2..a2d20c3 100644
--- a/clang/test/Misc/target-invalid-cpu-note.c
+++ b/clang/test/Misc/target-invalid-cpu-note.c
@@ -197,3 +197,11 @@
 // RUN: not %clang_cc1 -triple riscv64 -target-cpu not-a-cpu -fsyntax-only %s 2>&1 | FileCheck %s --check-prefix RISCV64
 // RISCV64: error: unknown target CPU 'not-a-cpu'
 // RISCV64: note: valid target CPU values are: generic-rv64, rocket-rv64, sifive-7-rv64, sifive-u54, sifive-u74
+
+// RUN: not %clang_cc1 -triple riscv32 -tune-cpu not-a-cpu -fsyntax-only %s 2>&1 | FileCheck %s --check-prefix TUNE-RISCV32
+// TUNE-RISCV32: error: unknown target CPU 'not-a-cpu'
+// TUNE-RISCV32: note: valid target CPU values are: generic-rv32, rocket-rv32, sifive-7-rv32, sifive-e31, sifive-e76, generic, rocket, sifive-7-series
+
+// RUN: not %clang_cc1 -triple riscv64 -tune-cpu not-a-cpu -fsyntax-only %s 2>&1 | FileCheck %s --check-prefix TUNE-RISCV64
+// TUNE-RISCV64: error: unknown target CPU 'not-a-cpu'
+// TUNE-RISCV64: note: valid target CPU values are: generic-rv64, rocket-rv64, sifive-7-rv64, sifive-u54, sifive-u74, generic, rocket, sifive-7-series