Start adding an `aarch64-pc-windows-msvc` target

This commit adds the necessary definitions for target specs and such as well as
the necessary support in libstd to compile basic `aarch64-pc-windows-msvc`
binaries. The target is not currently built on CI, but it can be built locally
with:

    ./configure --target=aarch64-pc-windows-msvc --set rust.lld
    ./x.py build src/libstd --target aarch64-pc-windows-msvc

Currently this fails to build `libtest` due to a linker bug (seemingly in LLD?)
which hasn't been investigate yet. Otherwise though with libstd you can build a
hello world program (linked with LLD). I've not tried to execute it yet, but it
at least links!

Full support for this target is still a long road ahead, but this is hopefully a
good stepping stone to get started.

Points of note about this target are:

* Currently defaults to `panic=abort` as support is still landing in LLVM for
  SEH on AArch64.
* Currently defaults to LLD as a linker as I was able to get farther with it
  than I was with `link.exe`

1 files changed, 63 insertions, 1 deletions

diff --git a/src/libstd/sys/windows/c.rs b/src/libstd/sys/windows/c.rs
index 6f81afe66f9..e514a56dcc4 100644
--- a/src/libstd/sys/windows/c.rs
+++ b/src/libstd/sys/windows/c.rs
@@ -280,6 +280,9 @@ pub const IMAGE_FILE_MACHINE_I386: DWORD = 0x014c;
 #[cfg(target_arch = "x86_64")]
 #[cfg(feature = "backtrace")]
 pub const IMAGE_FILE_MACHINE_AMD64: DWORD = 0x8664;
+#[cfg(target_arch = "aarch64")]
+#[cfg(feature = "backtrace")]
+pub const IMAGE_FILE_MACHINE_ARM64: DWORD = 0xAA64;
 
 pub const EXCEPTION_CONTINUE_SEARCH: LONG = 0;
 pub const EXCEPTION_STACK_OVERFLOW: DWORD = 0xc00000fd;
@@ -791,9 +794,68 @@ pub struct FLOATING_SAVE_AREA {
 // will not appear in the final documentation. This should be also defined for
 // other architectures supported by Windows such as ARM, and for historical
 // interest, maybe MIPS and PowerPC as well.
-#[cfg(all(dox, not(any(target_arch = "x86_64", target_arch = "x86"))))]
+#[cfg(all(dox, not(any(target_arch = "x86_64", target_arch = "x86", target_arch = "aarch64"))))]
 pub enum CONTEXT {}
 
+#[cfg(target_arch = "aarch64")]
+pub const ARM64_MAX_BREAKPOINTS: usize = 8;
+
+#[cfg(target_arch = "aarch64")]
+pub const ARM64_MAX_WATCHPOINTS: usize = 2;
+
+#[cfg(target_arch = "aarch64")]
+#[repr(C)]
+pub struct ARM64_NT_NEON128 {
+    pub D: [f64; 2],
+}
+
+#[cfg(target_arch = "aarch64")]
+#[repr(C, align(16))]
+pub struct CONTEXT {
+    pub ContextFlags: DWORD,
+    pub Cpsr: DWORD,
+    pub X0: u64,
+    pub X1: u64,
+    pub X2: u64,
+    pub X3: u64,
+    pub X4: u64,
+    pub X5: u64,
+    pub X6: u64,
+    pub X7: u64,
+    pub X8: u64,
+    pub X9: u64,
+    pub X10: u64,
+    pub X11: u64,
+    pub X12: u64,
+    pub X13: u64,
+    pub X14: u64,
+    pub X15: u64,
+    pub X16: u64,
+    pub X17: u64,
+    pub X18: u64,
+    pub X19: u64,
+    pub X20: u64,
+    pub X21: u64,
+    pub X22: u64,
+    pub X23: u64,
+    pub X24: u64,
+    pub X25: u64,
+    pub X26: u64,
+    pub X27: u64,
+    pub X28: u64,
+    pub Fp: u64,
+    pub Lr: u64,
+    pub Sp: u64,
+    pub Pc: u64,
+    pub V: [ARM64_NT_NEON128; 32],
+    pub Fpcr: DWORD,
+    pub Fpsr: DWORD,
+    pub Bcr: [DWORD; ARM64_MAX_BREAKPOINTS],
+    pub Bvr: [DWORD; ARM64_MAX_BREAKPOINTS],
+    pub Wcr: [DWORD; ARM64_MAX_WATCHPOINTS],
+    pub Wvr: [DWORD; ARM64_MAX_WATCHPOINTS],
+}
+
 #[repr(C)]
 pub struct SOCKADDR_STORAGE_LH {
     pub ss_family: ADDRESS_FAMILY,