librustc_back: remove explicit linker

"cc" is already the default.

src/librustc_back/target/apple_base.rs

@@ -35,7 +35,6 @@ pub fn opts() -> TargetOptions {
     TargetOptions {
         // OSX has -dead_strip, which doesn't rely on ffunction_sections
         function_sections: false,
-        linker: "cc".to_string(),
         dynamic_linking: true,
         executables: true,
         is_like_osx: true,

src/librustc_back/target/bitrig_base.rs

@@ -13,7 +13,6 @@ use std::default::Default;
 
 pub fn opts() -> TargetOptions {
     TargetOptions {
-        linker: "cc".to_string(),
         dynamic_linking: true,
         executables: true,
         linker_is_gnu: true,

src/librustc_back/target/dragonfly_base.rs

@@ -13,7 +13,6 @@ use std::default::Default;
 
 pub fn opts() -> TargetOptions {
     TargetOptions {
-        linker: "cc".to_string(),
         dynamic_linking: true,
         executables: true,
         linker_is_gnu: true,

src/librustc_back/target/freebsd_base.rs

@@ -13,7 +13,6 @@ use std::default::Default;
 
 pub fn opts() -> TargetOptions {
     TargetOptions {
-        linker: "cc".to_string(),
         dynamic_linking: true,
         executables: true,
         linker_is_gnu: true,

src/librustc_back/target/netbsd_base.rs

@@ -13,7 +13,6 @@ use std::default::Default;
 
 pub fn opts() -> TargetOptions {
     TargetOptions {
-        linker: "cc".to_string(),
         dynamic_linking: true,
         executables: true,
         linker_is_gnu: true,

src/librustc_back/target/openbsd_base.rs

@@ -13,7 +13,6 @@ use std::default::Default;
 
 pub fn opts() -> TargetOptions {
     TargetOptions {
-        linker: "cc".to_string(),
         dynamic_linking: true,
         executables: true,
         linker_is_gnu: true,

src/librustc_back/target/solaris_base.rs

@@ -13,7 +13,6 @@ use std::default::Default;
 
 pub fn opts() -> TargetOptions {
     TargetOptions {
-        linker: "cc".to_string(),
         dynamic_linking: true,
         executables: true,
         has_rpath: true,