aarch64-linux: Default to FramePointer::NonLeaf

For aarch64-apple and aarch64-windows, platform docs state that code
must use frame pointers correctly. This is because the AAPCS64 mandates
that a platform specify its frame pointer conformance requirements:
- Apple: https://developer.apple.com/documentation/xcode/writing-arm64-code-for-apple-platforms#Respect-the-purpose-of-specific-CPU-registers
- Windows: https://learn.microsoft.com/en-us/cpp/build/arm64-windows-abi-conventions?view=msvc-170#integer-registers
- AAPCS64: 4492d1570e/aapcs64/aapcs64.rst (the-frame-pointer)

Unwinding code either requires unwind tables or frame pointers, and
on aarch64 the expectation is that one can use frame pointers for this.
Most Linux targets represent a motley variety of possible distributions,
so it is unclear who to defer to on conformance, other than perhaps Arm.
In the absence of a specific edict for a given aarch64-linux target,
Rust will assume aarch64-linux targets use non-leaf frame pointers.
This reflects what compilers like clang do.

tests/codegen/frame-pointer.rs

@@ -26,8 +26,10 @@ pub fn peach(x: u32) -> u32 {
 
 // CHECK: attributes [[PEACH_ATTRS]] = {
 // x64-linux-NOT: {{.*}}"frame-pointer"{{.*}}
-// aarch64-linux-NOT: {{.*}}"frame-pointer"{{.*}}
 // x64-apple-SAME: {{.*}}"frame-pointer"="all"
 // force-SAME: {{.*}}"frame-pointer"="all"
+//
+// AAPCS64 demands frame pointers:
+// aarch64-linux-SAME: {{.*}}"frame-pointer"="non-leaf"
 // aarch64-apple-SAME: {{.*}}"frame-pointer"="non-leaf"
 // CHECK-SAME: }