[NetBSD] Use cortex-a8 as default CPU for ARMv7

This matches the platform default for GCC. It primarily matters when the
integrated assembler is not used as there is no default CPU defined for
ARMv7-A and GNU as is upset with -mcpu=generic.

clang/test/Driver/netbsd.c

@@ -236,6 +236,7 @@
 // ARMEB: "{{.*}}/usr/lib{{/|\\\\}}eabi{{/|\\\\}}crti.o"
 // ARMEB: "{{.*}}/usr/lib{{/|\\\\}}crtbegin.o" "{{.*}}.o" "-lc"
 // ARMEB: "{{.*}}/usr/lib{{/|\\\\}}crtend.o" "{{.*}}/usr/lib{{/|\\\\}}crtn.o"
+// ARMV7EB: as{{.*}}" "-mcpu=cortex-a8"
 // ARMV7EB: ld{{.*}}" "--eh-frame-hdr" "-dynamic-linker" "/libexec/ld.elf_so"
 // ARMV7EB: "--be8" "-m" "armelfb_nbsd_eabi"
 

llvm/lib/Support/Triple.cpp

@@ -1699,6 +1699,8 @@ StringRef Triple::getARMCPUForArch(StringRef MArch) const {
   case llvm::Triple::NetBSD:
     if (!MArch.empty() && MArch == "v6")
       return "arm1176jzf-s";
+    if (!MArch.empty() && MArch == "v7")
+      return "cortex-a8";
     break;
   case llvm::Triple::Win32:
     // FIXME: this is invalid for WindowsCE