trans: Move rust_try into the compiler

This commit moves the IR files in the distribution, rust_try.ll,
rust_try_msvc_64.ll, and rust_try_msvc_32.ll into the compiler from the main
distribution. There's a few reasons for this change:

* LLVM changes its IR syntax from time to time, so it's very difficult to
  have these files build across many LLVM versions simultaneously. We'll likely
  want to retain this ability for quite some time into the future.
* The implementation of these files is closely tied to the compiler and runtime
  itself, so it makes sense to fold it into a location which can do more
  platform-specific checks for various implementation details (such as MSVC 32
  vs 64-bit).
* This removes LLVM as a build-time dependency of the standard library. This may
  end up becoming very useful if we move towards building the standard library
  with Cargo.

In the immediate future, however, this commit should restore compatibility with
LLVM 3.5 and 3.6.

src/libcore/intrinsics.rs

@@ -602,4 +602,10 @@ extern "rust-intrinsic" {
     /// Returns the value of the discriminant for the variant in 'v',
     /// cast to a `u64`; if `T` has no discriminant, returns 0.
     pub fn discriminant_value<T>(v: &T) -> u64;
+
+    /// Rust's "try catch" construct which invokes the function pointer `f` with
+    /// the data pointer `data`, returning the exception payload if an exception
+    /// is thrown (aka the thread panics).
+    #[cfg(not(stage0))]
+    pub fn try(f: fn(*mut u8), data: *mut u8) -> *mut u8;
 }