Use "x86-64" as the target CPU for NetBSD and Bitrig on amd64.

Using "generic" disables a number of features that are present on all
x86_64 cpus, the "x86-64" target cpu is the common denominator for that
arch.

Refs #20777

Author: jakllsch

src/librustc_back/target/x86_64_rumprun_netbsd.rs

@@ -12,6 +12,7 @@ use target::Target;
 
 pub fn target() -> Target {
     let mut base = super::netbsd_base::opts();
+    base.cpu = "x86-64".to_string();
     base.pre_link_args.push("-m64".to_string());
     base.linker = "x86_64-rumprun-netbsd-gcc".to_string();
     base.ar = "x86_64-rumprun-netbsd-ar".to_string();

src/librustc_back/target/x86_64_unknown_bitrig.rs

@@ -12,6 +12,7 @@ use target::Target;
 
 pub fn target() -> Target {
     let mut base = super::bitrig_base::opts();
+    base.cpu = "x86-64".to_string();
     base.max_atomic_width = 64;
     base.pre_link_args.push("-m64".to_string());
 

src/librustc_back/target/x86_64_unknown_netbsd.rs

@@ -12,6 +12,7 @@ use target::Target;
 
 pub fn target() -> Target {
     let mut base = super::netbsd_base::opts();
+    base.cpu = "x86-64".to_string();
     base.max_atomic_width = 64;
     base.pre_link_args.push("-m64".to_string());