Fail to build LDC2 on Windows 7 X64

[Kai Nacke]

Hi Zhouxuan!

> A minor issue about those instructions in the url is, both "git 
> checkout -b ldc" in section "Build LDC2" failed as ldc branch 
> already exists, just removing -b option works for me.

Indeed, this section can be simplified. I am going to update the 
instructions.

> Another instruction confuse me is that, 
> -DLLVM_TARGETS_TO_BUILD="X86" option to cmake while generating 
> Win64 project files, is X86 instead of X64 here correct?

Yes, X86 is right. It includes the 32bit and 64bit targets for 
Intel/AMD.

There is also PowerPC for 32bit and 64bit PowerPC targets. But is 
no general rule: target ARM is for ARMv7 (32bit) and target 
AArch64 is for ARMv8 (64bit).

Regards
Kai