Set max-atomic-width for armv4 and armv5 to zero, to disable atomics

Author: thejpster

compiler/rustc_target/src/spec/targets/armv4t_none_eabi.rs

@@ -29,6 +29,7 @@ pub(crate) fn target() -> Target {
             asm_args: cvs!["-mthumb-interwork", "-march=armv4t", "-mlittle-endian",],
             features: "+soft-float,+strict-align".into(),
             atomic_cas: false,
+            max_atomic_width: Some(0),
             has_thumb_interworking: true,
             ..base::arm_none::opts()
         },

compiler/rustc_target/src/spec/targets/armv5te_none_eabi.rs

@@ -20,6 +20,7 @@ pub(crate) fn target() -> Target {
             asm_args: cvs!["-mthumb-interwork", "-march=armv5te", "-mlittle-endian",],
             features: "+soft-float,+strict-align".into(),
             atomic_cas: false,
+            max_atomic_width: Some(0),
             has_thumb_interworking: true,
             ..base::arm_none::opts()
         },

compiler/rustc_target/src/spec/targets/thumbv4t_none_eabi.rs

@@ -29,6 +29,7 @@ pub(crate) fn target() -> Target {
             asm_args: cvs!["-mthumb-interwork", "-march=armv4t", "-mlittle-endian",],
             features: "+soft-float,+strict-align".into(),
             atomic_cas: false,
+            max_atomic_width: Some(0),
             has_thumb_interworking: true,
             ..base::arm_none::opts()
         },

compiler/rustc_target/src/spec/targets/thumbv5te_none_eabi.rs

@@ -20,6 +20,7 @@ pub(crate) fn target() -> Target {
             asm_args: cvs!["-mthumb-interwork", "-march=armv5te", "-mlittle-endian",],
             features: "+soft-float,+strict-align".into(),
             atomic_cas: false,
+            max_atomic_width: Some(0),
             has_thumb_interworking: true,
             ..base::arm_none::opts()
         },