Turn off frame pointer elimination on all Apple platforms.

This ends up disabling frame pointer elimination on aarch64_apple_darwin
which matches what clang does by default along with the
aarch64_apple_ios and x86_64_apple_darwin targets.

Further, the Apple docs "Writing ARM64 Code for Apple Platforms" has a section
called "Respect the Purpose of Specific CPU Registers" which
specifically calls out the frame pointer register (x29):

   The frame pointer register (x29) must always address a valid frame
   record. Some functions — such as leaf functions or tail calls — may
   opt not to create an entry in this list As a result, stack traces
   are always meaningful, even without debug information.

Other platforms are updated to not override the default.

compiler/rustc_target/src/spec/aarch64_apple_ios.rs

@@ -10,7 +10,6 @@ pub fn target() -> Target {
         arch: "aarch64".to_string(),
         options: TargetOptions {
             features: "+neon,+fp-armv8,+apple-a7".to_string(),
-            eliminate_frame_pointer: false,
             max_atomic_width: Some(128),
             unsupported_abis: super::arm_base::unsupported_abis(),
             forces_embed_bitcode: true,

compiler/rustc_target/src/spec/aarch64_apple_ios_macabi.rs

@@ -10,7 +10,6 @@ pub fn target() -> Target {
         arch: "aarch64".to_string(),
         options: TargetOptions {
             features: "+neon,+fp-armv8,+apple-a12".to_string(),
-            eliminate_frame_pointer: false,
             max_atomic_width: Some(128),
             unsupported_abis: super::arm_base::unsupported_abis(),
             forces_embed_bitcode: true,

compiler/rustc_target/src/spec/aarch64_apple_ios_sim.rs

@@ -18,7 +18,6 @@ pub fn target() -> Target {
         arch: "aarch64".to_string(),
         options: TargetOptions {
             features: "+neon,+fp-armv8,+apple-a7".to_string(),
-            eliminate_frame_pointer: false,
             max_atomic_width: Some(128),
             unsupported_abis: super::arm_base::unsupported_abis(),
             forces_embed_bitcode: true,

compiler/rustc_target/src/spec/aarch64_apple_tvos.rs

@@ -10,7 +10,6 @@ pub fn target() -> Target {
         arch: "aarch64".to_string(),
         options: TargetOptions {
             features: "+neon,+fp-armv8,+apple-a7".to_string(),
-            eliminate_frame_pointer: false,
             max_atomic_width: Some(128),
             unsupported_abis: super::arm_base::unsupported_abis(),
             forces_embed_bitcode: true,

compiler/rustc_target/src/spec/apple_base.rs

@@ -27,6 +27,7 @@ pub fn opts(os: &str) -> TargetOptions {
         families: vec!["unix".to_string()],
         is_like_osx: true,
         dwarf_version: Some(2),
+        eliminate_frame_pointer: false,
         has_rpath: true,
         dll_suffix: ".dylib".to_string(),
         archive_format: "darwin".to_string(),

compiler/rustc_target/src/spec/apple_sdk_base.rs

@@ -44,7 +44,6 @@ pub fn opts(os: &str, arch: Arch) -> TargetOptions {
         executables: true,
         link_env_remove: link_env_remove(arch),
         has_elf_tls: false,
-        eliminate_frame_pointer: false,
         ..super::apple_base::opts(os)
     }
 }