Implement an `address_insignificant` attribute

This can be applied to statics and it will indicate that LLVM will attempt to
merge the constant in .data with other statics.

I have preliminarily applied this to all of the statics generated by the new
`ifmt!` syntax extension. I compiled a file with 1000 calls to `ifmt!` and a
separate file with 1000 calls to `fmt!` to compare the sizes, and the results
were:

fmt           310k
ifmt (before) 529k
ifmt (after)  202k

This now means that ifmt! is both faster and smaller than fmt!, yay!

1 files changed, 4 insertions, 0 deletions

diff --git a/src/rustllvm/RustWrapper.cpp b/src/rustllvm/RustWrapper.cpp
index 04c062072d6..db353036336 100644
--- a/src/rustllvm/RustWrapper.cpp
+++ b/src/rustllvm/RustWrapper.cpp
@@ -833,3 +833,7 @@ extern "C" LLVMValueRef LLVMDIBuilderCreateUnionType(
         unwrapDI<DIArray>(Elements),
         RunTimeLang));
 }
+
+extern "C" void LLVMSetUnnamedAddr(LLVMValueRef Value, LLVMBool Unnamed) {
+    unwrap<GlobalValue>(Value)->setUnnamedAddr(Unnamed);
+}