Move sys_can_stack_trace from GPA to std.debug so that it can be re-used as needed

lib/std/debug.zig

@@ -26,6 +26,27 @@ pub const runtime_safety = switch (builtin.mode) {
     .ReleaseFast, .ReleaseSmall => false,
 };
 
+pub const sys_can_stack_trace = switch (builtin.cpu.arch) {
+    // Observed to go into an infinite loop.
+    // TODO: Make this work.
+    .mips,
+    .mipsel,
+    => false,
+
+    // `@returnAddress()` in LLVM 10 gives
+    // "Non-Emscripten WebAssembly hasn't implemented __builtin_return_address".
+    .wasm32,
+    .wasm64,
+    => builtin.os.tag == .emscripten,
+
+    // `@returnAddress()` is unsupported in LLVM 13.
+    .bpfel,
+    .bpfeb,
+    => false,
+
+    else => true,
+};
+
 pub const LineInfo = struct {
     line: u64,
     column: u64,

lib/std/heap/general_purpose_allocator.zig

@@ -105,28 +105,8 @@ const StackTrace = std.builtin.StackTrace;
 /// Integer type for pointing to slots in a small allocation
 const SlotIndex = std.meta.Int(.unsigned, math.log2(page_size) + 1);
 
-const sys_can_stack_trace = switch (builtin.cpu.arch) {
-    // Observed to go into an infinite loop.
-    // TODO: Make this work.
-    .mips,
-    .mipsel,
-    => false,
-
-    // `@returnAddress()` in LLVM 10 gives
-    // "Non-Emscripten WebAssembly hasn't implemented __builtin_return_address".
-    .wasm32,
-    .wasm64,
-    => builtin.os.tag == .emscripten,
-
-    // `@returnAddress()` is unsupported in LLVM 13.
-    .bpfel,
-    .bpfeb,
-    => false,
-
-    else => true,
-};
 const default_test_stack_trace_frames: usize = if (builtin.is_test) 8 else 4;
-const default_sys_stack_trace_frames: usize = if (sys_can_stack_trace) default_test_stack_trace_frames else 0;
+const default_sys_stack_trace_frames: usize = if (std.debug.sys_can_stack_trace) default_test_stack_trace_frames else 0;
 const default_stack_trace_frames: usize = switch (builtin.mode) {
     .Debug => default_sys_stack_trace_frames,
     else => 0,

lib/std/testing/failing_allocator.zig

@@ -19,9 +19,11 @@ pub const FailingAllocator = struct {
     freed_bytes: usize,
     allocations: usize,
     deallocations: usize,
-    stack_addresses: [16]usize,
+    stack_addresses: [num_stack_frames]usize,
     has_induced_failure: bool,
 
+    const num_stack_frames = if (std.debug.sys_can_stack_trace) 16 else 0;
+
     /// `fail_index` is the number of successful allocations you can
     /// expect from this allocator. The next allocation will fail.
     /// For example, if this is called with `fail_index` equal to 2,