Configure LLVM module PIC level

As of LLVM 9, this is required for 32-bit PowerPC to properly generate
PLT references. Previously, only BigPIC was supported; now LLVM supports
both BigPIC and SmallPIC, and there is no default value provided.

src/librustc_codegen_llvm/context.rs

@@ -203,6 +203,10 @@ pub unsafe fn create_module(
     let llvm_target = SmallCStr::new(&sess.target.target.llvm_target);
     llvm::LLVMRustSetNormalizedTarget(llmod, llvm_target.as_ptr());
 
+    if get_reloc_model(sess) == llvm::RelocMode::PIC {
+        llvm::LLVMRustSetModulePICLevel(llmod);
+    }
+
     if is_pie_binary(sess) {
         llvm::LLVMRustSetModulePIELevel(llmod);
     }

src/librustc_codegen_llvm/llvm/ffi.rs

@@ -1805,6 +1805,7 @@ extern "C" {
 
     pub fn LLVMRustSetComdat(M: &'a Module, V: &'a Value, Name: *const c_char);
     pub fn LLVMRustUnsetComdat(V: &Value);
+    pub fn LLVMRustSetModulePICLevel(M: &Module);
     pub fn LLVMRustSetModulePIELevel(M: &Module);
     pub fn LLVMRustModuleBufferCreate(M: &Module) -> &'static mut ModuleBuffer;
     pub fn LLVMRustModuleBufferPtr(p: &ModuleBuffer) -> *const u8;

src/rustllvm/PassWrapper.cpp

@@ -754,6 +754,10 @@ LLVMRustSetDataLayoutFromTargetMachine(LLVMModuleRef Module,
   unwrap(Module)->setDataLayout(Target->createDataLayout());
 }
 
+extern "C" void LLVMRustSetModulePICLevel(LLVMModuleRef M) {
+  unwrap(M)->setPICLevel(PICLevel::Level::BigPIC);
+}
+
 extern "C" void LLVMRustSetModulePIELevel(LLVMModuleRef M) {
   unwrap(M)->setPIELevel(PIELevel::Level::Large);
 }