Build with LLVM 3.6 broken on HEAD

[sanxiyn]

Since #27076, build with LLVM 3.6 is broken on HEAD.

$ make
compile: x86_64-unknown-linux-gnu/rt/rust_try.o
/usr/lib/llvm-3.6/bin/llc: /development/sanxiyn/rust/src/rt/rust_try.ll:18:5: error: expected '{' in function body
    personality i8* bitcast (i32 (...)* @rust_eh_personality_catch to i8*)
    ^

[brson]

Yes, that's right. To fix this will take duplicating these bits of LLVM IR.

[brson]

@alexcrichton has the fix.