[Clang][LoongArch] Add initial LoongArch target and driver support

With the initial support added, clang can compile `helloworld` C
to executable file for loongarch64. For example:

```
$ cat hello.c
int main() {
  printf("Hello, world!\n");
  return 0;
}
$ clang --target=loongarch64-unknown-linux-gnu --gcc-toolchain=xxx --sysroot=xxx hello.c
```

The output a.out can run within qemu or native machine. For example:

```
$ file ./a.out
./a.out: ELF 64-bit LSB pie executable, LoongArch, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-loongarch-lp64d.so.1, for GNU/Linux 5.19.0, with debug_info, not stripped
$ ./a.out
Hello, world!
```

Currently gcc toolchain and sysroot can be found here:
https://github.com/loongson/build-tools/releases/download/2022.08.11/loongarch64-clfs-5.1-cross-tools-gcc-glibc.tar.xz

Reference: https://github.com/loongson/LoongArch-Documentation
The last commit hash (main branch) is:
99016636af64d02dee05e39974d4c1e55875c45b

Note loongarch32 is not fully tested because there is no reference
gcc toolchain yet.

Differential Revision: https://reviews.llvm.org/D130255

1 files changed, 15 insertions, 0 deletions

diff --git a/clang/lib/Basic/Targets.cpp b/clang/lib/Basic/Targets.cpp
index 2d6ef99..3824480 100644
--- a/clang/lib/Basic/Targets.cpp
+++ b/clang/lib/Basic/Targets.cpp
@@ -24,6 +24,7 @@
 #include "Targets/Hexagon.h"
 #include "Targets/Lanai.h"
 #include "Targets/Le64.h"
+#include "Targets/LoongArch.h"
 #include "Targets/M68k.h"
 #include "Targets/MSP430.h"
 #include "Targets/Mips.h"
@@ -670,6 +671,20 @@ TargetInfo *AllocateTarget(const llvm::Triple &Triple,
     default:
       return new CSKYTargetInfo(Triple, Opts);
     }
+  case llvm::Triple::loongarch32:
+    switch (os) {
+    case llvm::Triple::Linux:
+      return new LinuxTargetInfo<LoongArch32TargetInfo>(Triple, Opts);
+    default:
+      return new LoongArch32TargetInfo(Triple, Opts);
+    }
+  case llvm::Triple::loongarch64:
+    switch (os) {
+    case llvm::Triple::Linux:
+      return new LinuxTargetInfo<LoongArch64TargetInfo>(Triple, Opts);
+    default:
+      return new LoongArch64TargetInfo(Triple, Opts);
+    }
   }
 }
 } // namespace targets