rustc: Implement stack probes for x86

This commit implements stack probes on x86/x86_64 using the freshly landed
support upstream in LLVM. The purpose of stack probes here are to guarantee a
segfault on stack overflow rather than having a chance of running over the guard
page already present on all threads by accident.

At this time there's no support for any other architecture because LLVM itself
does not have support for other architectures.

Author: alexcrichton

src/libcompiler_builtins

@@ -26,6 +26,7 @@ pub fn target() -> TargetResult {
         linker_flavor: LinkerFlavor::Gcc,
         options: TargetOptions {
             max_atomic_width: Some(64),
+            stack_probes: true,
             .. base
         }
     })

src/librustc_back/target/i386_apple_ios.rs

@@ -16,6 +16,7 @@ pub fn target() -> TargetResult {
     base.cpu = "yonah".to_string();
     base.max_atomic_width = Some(64);
     base.pre_link_args.insert(LinkerFlavor::Gcc, vec!["-m32".to_string()]);
+    base.stack_probes = true;
 
     Ok(Target {
         llvm_target: "i686-apple-darwin".to_string(),

src/librustc_back/target/i686_apple_darwin.rs

@@ -22,6 +22,7 @@ pub fn target() -> TargetResult {
     // http://developer.android.com/ndk/guides/abis.html#x86
     base.cpu = "pentiumpro".to_string();
     base.features = "+mmx,+sse,+sse2,+sse3,+ssse3".to_string();
+    base.stack_probes = true;
 
     Ok(Target {
         llvm_target: "i686-linux-android".to_string(),

src/librustc_back/target/i686_linux_android.rs

@@ -16,6 +16,7 @@ pub fn target() -> TargetResult {
     base.cpu = "pentium4".to_string();
     base.max_atomic_width = Some(64);
     base.pre_link_args.get_mut(&LinkerFlavor::Gcc).unwrap().push("-m32".to_string());
+    base.stack_probes = true;
 
     Ok(Target {
         llvm_target: "i686-unknown-dragonfly".to_string(),

src/librustc_back/target/i686_unknown_dragonfly.rs

@@ -16,6 +16,7 @@ pub fn target() -> TargetResult {
     base.cpu = "pentium4".to_string();
     base.max_atomic_width = Some(64);
     base.pre_link_args.get_mut(&LinkerFlavor::Gcc).unwrap().push("-m32".to_string());
+    base.stack_probes = true;
 
     Ok(Target {
         llvm_target: "i686-unknown-freebsd".to_string(),

src/librustc_back/target/i686_unknown_freebsd.rs

@@ -16,6 +16,7 @@ pub fn target() -> TargetResult {
     base.cpu = "pentium4".to_string();
     base.max_atomic_width = Some(64);
     base.pre_link_args.insert(LinkerFlavor::Gcc, vec!["-m32".to_string()]);
+    base.stack_probes = true;
 
     Ok(Target {
         llvm_target: "i686-unknown-haiku".to_string(),

src/librustc_back/target/i686_unknown_haiku.rs

@@ -16,6 +16,7 @@ pub fn target() -> TargetResult {
     base.cpu = "pentium4".to_string();
     base.max_atomic_width = Some(64);
     base.pre_link_args.get_mut(&LinkerFlavor::Gcc).unwrap().push("-m32".to_string());
+    base.stack_probes = true;
 
     Ok(Target {
         llvm_target: "i686-unknown-linux-gnu".to_string(),

src/librustc_back/target/i686_unknown_linux_gnu.rs

@@ -17,6 +17,7 @@ pub fn target() -> TargetResult {
     base.max_atomic_width = Some(64);
     base.pre_link_args.get_mut(&LinkerFlavor::Gcc).unwrap().push("-m32".to_string());
     base.pre_link_args.get_mut(&LinkerFlavor::Gcc).unwrap().push("-Wl,-melf_i386".to_string());
+    base.stack_probes = true;
 
     // The unwinder used by i686-unknown-linux-musl, the LLVM libunwind
     // implementation, apparently relies on frame pointers existing... somehow.

src/librustc_back/target/i686_unknown_linux_musl.rs

@@ -16,6 +16,7 @@ pub fn target() -> TargetResult {
     base.cpu = "pentium4".to_string();
     base.max_atomic_width = Some(64);
     base.pre_link_args.get_mut(&LinkerFlavor::Gcc).unwrap().push("-m32".to_string());
+    base.stack_probes = true;
 
     Ok(Target {
         llvm_target: "i686-unknown-netbsdelf".to_string(),