Add 'native' to -C target-cpu=help

[mattico]

Fixes #44393

[rust-highfive]

r? @aturon

(rust_highfive has picked a reviewer for you, use r? to override)

[mattico]

Bump

[arielb1]

Is there an easy way to add the current native CPU. i.e., to make the message look like:

    native - Select the CPU of the current host (currently core2).

[arielb1]

I'm ok with r+-ing this PR as it is, but I think the change above could be an improvement.

[mattico]

Another idea: If we're cross compiling then we probably don't want to print this info, since it'll be wrong/misleading.

[mattico]

λ build\x86_64-pc-windows-msvc\stage1\bin\rustc -C target-cpu=help
Available CPUs for this target:
    native         - Select the CPU of the current host (currently haswell).
    amdfam10       - Select the amdfam10 processor.
    athlon         - Select the athlon processor.
<snip>
λ build\x86_64-pc-windows-msvc\stage1\bin\rustc -C target-cpu=help --target arm-unknown-linux-gnueabi
Available CPUs for this target:
    arm1020e      - Select the arm1020e processor.
    arm1020t      - Select the arm1020t processor.
<snip>

[mattico]

r? @arielb1

[arielb1]

@bors r+

[bors]

📌 Commit e04c54e has been approved by arielb1

[bors]

⌛ Testing commit e04c54e86d899e9a213cfef006c2f7d4268db0b7 with merge 81922065dcf1e86ce4929112535f352f698dfcbf...

[bors]

💔 Test failed - status-travis

[kennytm]

Failed to build rustc_llvm on dist-x86_64-linux alt.

[00:07:21] cargo:warning=../rustllvm/PassWrapper.cpp: In function 'void LLVMRustPrintTargetCPUs(LLVMTargetMachineRef)':
[00:07:21] cargo:warning=../rustllvm/PassWrapper.cpp:310:55: error: cannot pass objects of non-trivially-copyable type 'std::string {aka class std::basic_string<char>}' through '...'
[00:07:21] cargo:warning=       MaxCPULen, "native", sys::getHostCPUName().str());
[00:07:21] cargo:warning=                                                       ^
[00:07:21] cargo:warning=../rustllvm/PassWrapper.cpp:310:55: warning: format '%s' expects argument of type 'char*', but argument 4 has type 'std::string {aka std::basic_string<char>}' [-Wformat=]

[hanna-kruppe]

StringRefs are not guaranteed to be null terminated. Use %.*s and pass the length as well, as in

rust/src/rustllvm/PassWrapper.cpp

Lines 651 to 655 in 5dfc84c

	// These unsigned->signed casts could theoretically overflow, but
	// realistically never will (and even if, the result is implementation
	// defined rather plain UB).
	printf("%15.*s - %.*s\n", (int)PassArg.size(), PassArg.data(),
	(int)PassName.size(), PassName.data());

[alexcrichton]

@bors: r=arielb1

[bors]

📌 Commit 824fb38 has been approved by arielb1

[bors]

⌛ Testing commit 824fb38 with merge 4cdb362...

[bors]

☀️ Test successful - status-appveyor, status-travis
Approved by: arielb1
Pushing 4cdb362 to master...