gh-124043: Disallow mixing `--with-trace-refs` and `--disable-gil` (#124078)

Tracing references is not currently thread-safe in the free-threaded build.

Misc/NEWS.d/next/Build/2024-09-13-17-48-37.gh-issue-124043.Bruxpq.rst

@@ -0,0 +1,2 @@
+Building using :option:`--with-trace-refs` is (temporarily) disallowed when the
+GIL is disabled.

configure

@@ -8234,6 +8234,10 @@ printf "%s\n" "#define Py_TRACE_REFS 1" >>confdefs.h
 
 fi
 
+if test "$disable_gil" = "yes" -a "$with_trace_refs" = "yes";
+then
+  as_fn_error $? "--disable-gil cannot be used with --with-trace-refs" "$LINENO" 5
+fi
 
 # Check for --enable-pystats
 { printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking for --enable-pystats" >&5

configure.ac

@@ -1777,6 +1777,10 @@ then
             [Define if you want to enable tracing references for debugging purpose])
 fi
 
+if test "$disable_gil" = "yes" -a "$with_trace_refs" = "yes";
+then
+  AC_MSG_ERROR([--disable-gil cannot be used with --with-trace-refs])
+fi
 
 # Check for --enable-pystats
 AC_MSG_CHECKING([for --enable-pystats])