SCons: Refactor handling of production flag and per-platform LTO defaults

Fixup to #63288.
See #65583 for the bug report.

Co-authored-by: Cyberrebell <chainsaw75@web.de>

platform/macos/detect.py

@@ -40,9 +40,6 @@ def get_flags():
     return [
         ("arch", detect_arch()),
         ("use_volk", False),
-        # Benefits of LTO for macOS (size, performance) haven't been clearly established yet.
-        # So for now we override the default value which may be set when using `production=yes`.
-        ("lto", "none"),
     ]
 
 
@@ -170,6 +167,10 @@ def configure(env):
         env["AS"] = basecmd + "as"
 
     # LTO
+
+    if env["lto"] == "auto":  # LTO benefits for macOS (size, performance) haven't been clearly established yet.
+        env["lto"] = "none"
+
     if env["lto"] != "none":
         if env["lto"] == "thin":
             env.Append(CCFLAGS=["-flto=thin"])
@@ -178,6 +179,8 @@ def configure(env):
             env.Append(CCFLAGS=["-flto"])
             env.Append(LINKFLAGS=["-flto"])
 
+    # Sanitizers
+
     if env["use_ubsan"] or env["use_asan"] or env["use_tsan"]:
         env.extra_suffix += ".san"
         env.Append(CCFLAGS=["-DSANITIZERS_ENABLED"])