Add bindings for LLVM methods:

1. LLVMGetFirstFunction
2. LLVMGetNextFunction
3. LLVMGetModuleContext
4. LLVMAddAttributeAtIndex

Author: Shourya742

compiler/rustc_codegen_llvm/src/llvm/ffi.rs

@@ -609,6 +609,8 @@ pub(crate) enum ArchiveKind {
     K_AIXBIG,
 }
 
+pub(crate) const LLVMAttributeFunctionIndex: c_uint = 0;
+
 unsafe extern "C" {
     // LLVMRustThinLTOData
     pub(crate) type ThinLTOData;
@@ -1157,6 +1159,12 @@ unsafe extern "C" {
     pub(crate) fn LLVMGetNamedGlobal(M: &Module, Name: *const c_char) -> Option<&Value>;
     pub(crate) fn LLVMGetFirstGlobal(M: &Module) -> Option<&Value>;
     pub(crate) fn LLVMGetNextGlobal(GlobalVar: &Value) -> Option<&Value>;
+
+    pub(crate) fn LLVMGetFirstFunction(M: &Module) -> Option<&Value>;
+    pub(crate) fn LLVMGetNextFunction(Fn: &Value) -> Option<&Value>;
+    pub(crate) fn LLVMGetModuleContext(M: &Module) -> &Context;
+    pub(crate) fn LLVMAddAttributeAtIndex(F: &Value, Idx: u32, A: &Attribute);
+
     pub(crate) fn LLVMDeleteGlobal(GlobalVar: &Value);
     pub(crate) fn LLVMGetInitializer(GlobalVar: &Value) -> Option<&Value>;
     pub(crate) fn LLVMSetInitializer<'a>(GlobalVar: &'a Value, ConstantVal: &'a Value);