Automatically use execinfo for crash handler on *BSD and musl-based Linux

[Calinou]

This closes #57193 and closes godotengine/godot-proposals#2439.

Tested on an Alpine Linux container (docker run -itv $PWD:/opt/godot alpine in a Godot repository clone, then install dependencies), it works as expected.

Unlike my glibc-based desktop, I get a crash on startup when running the project manager with --headless:

/opt/godot # bin/godot.linuxbsd.tools.64 --headless
Godot Engine v4.0.alpha.custom_build.e06a61b25 - https://godotengine.org

================================================================
handle_crash: Program crashed with signal 11
Engine version: Godot Engine v4.0.alpha.custom_build (e06a61b25877003aa53d5617d48012b93adb5ebd) 

Dumping the backtrace. Please include this when reporting the bug on: https://github.com/godotengine/godot/issues
-- END OF BACKTRACE --
================================================================
Aborted (core dumped)

--version works though:

/opt/godot # bin/godot.linuxbsd.tools.64 --version
4.0.alpha.custom_build.e06a61b25

[akien-mga]

I'd suggest instead:

diff --git a/platform/linuxbsd/detect.py b/platform/linuxbsd/detect.py
index 00e2b9e6eb..8c1b3cbfb6 100644
--- a/platform/linuxbsd/detect.py
+++ b/platform/linuxbsd/detect.py
@@ -382,7 +382,10 @@ def configure(env):
     if platform.system() == "Linux":
         env.Append(LIBS=["dl"])
 
-    if platform.system().find("BSD") >= 0:
+    if not env["execinfo"] and platform.libc_ver()[0] != "glibc":
+        # The default crash handler depends on glibc, so if the host uses
+        # a different libc (BSD libc, musl), fall back to libexecinfo.
+        print("Note: Using `execinfo=yes` for the crash handler as required on platforms where glibc is missing.")
         env["execinfo"] = True
 
     if env["execinfo"]:

Apparently CPython's platform.libc_ver() doesn't identify musl properly python/cpython#87414, but it returns a tuple of empty strings so this logic would work anyway as we only care to know that we're not running glibc.

A drawback to both proposed changes is that it might prevent cross-compiling for Linux-glibc from a BSD (existing issue) or musl (new issue) system. But that's very niche, we can address it if/when someone wants to do this (e.g. by making execinfo=<auto|yes|no>).

[Calinou]

@akien-mga I applied your suggestion and tested it locally, works well 🙂

[akien-mga]

Aside from last comment, should be good to merge.

[akien-mga]

Thanks!

[akien-mga]

Cherry-picked for 3.6.