Add no-plt as a compiler option

# Conflicts:
#	src/librustc/session/config.rs

Author: GabrielMajeri

src/librustc/session/config.rs

@@ -1387,6 +1387,9 @@ options! {DebuggingOptions, DebuggingSetter, basic_debugging_options,
           "output a json file with profiler results"),
     emit_stack_sizes: bool = (false, parse_bool, [UNTRACKED],
           "emits a section containing stack size metadata"),
+    no_plt: Option<bool> = (None, parse_opt_bool, [TRACKED],
+          "skip the PLT when calling into ELF shared libraries
+          (default: true if full relro is also enabled)"),
 }
 
 pub fn default_lib_output() -> CrateType {

src/librustc_codegen_llvm/attributes.rs

@@ -174,10 +174,12 @@ pub fn from_fn_attrs(
     set_frame_pointer_elimination(cx, llfn);
     set_probestack(cx, llfn);
 
-    // Only enable this optimization if full relro is also enabled.
-    // In this case, lazy binding was already unavailable, so nothing is lost.
-    if let RelroLevel::Full = cx.sess().target.target.options.relro_level {
-        Attribute::NonLazyBind.apply_llfn(Function, llfn);
+    if cx.sess().opts.debugging_opts.no_plt.unwrap_or(true) {
+        // Only enable this optimization if full relro is also enabled.
+        // In this case, lazy binding was already unavailable, so nothing is lost.
+        if let RelroLevel::Full = cx.sess().target.target.options.relro_level {
+            Attribute::NonLazyBind.apply_llfn(Function, llfn);
+        }
     }
 
     if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::COLD) {