fix: gate raw syscalls to Android, use sigprocmask elsewhere

libsigchain's sigprocmask guard is only active inside its own special
handlers, so our signal handler still gets filtered. Keep the raw
syscall on Android and use the standard sigprocmask on other platforms.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: jpnurmi

src/backends/sentry_backend_inproc.c

@@ -1565,12 +1565,17 @@ process_ucontext(const sentry_ucontext_t *uctx)
         uintptr_t sp = get_stack_pointer(uctx);
 
         // Mask the signal so SA_NODEFER doesn't let re-raises from the chained
-        // handler to kill the process before we regain control.
+        // handler kill the process before we regain control.
         sigset_t mask, old_mask;
         sigemptyset(&mask);
         sigaddset(&mask, uctx->signum);
-        // raw syscall to bypass libsigchain on Android
+#    ifdef SENTRY_PLATFORM_ANDROID
+        // Raw syscall to bypass libsigchain, whose sigprocmask guard
+        // is only active inside its own special handlers.
         syscall(SYS_rt_sigprocmask, SIG_BLOCK, &mask, &old_mask, _NSIG / 8);
+#    else
+        sigprocmask(SIG_BLOCK, &mask, &old_mask);
+#    endif
 
         // invoke the previous handler (typically the CLR/Mono
         // signal-to-managed-exception handler)
@@ -1599,7 +1604,11 @@ process_ucontext(const sentry_ucontext_t *uctx)
         syscall(SYS_rt_sigtimedwait, &mask, NULL, &timeout, _NSIG / 8);
 
         // unmask
+#    ifdef SENTRY_PLATFORM_ANDROID
         syscall(SYS_rt_sigprocmask, SIG_SETMASK, &old_mask, NULL, _NSIG / 8);
+#    else
+        sigprocmask(SIG_SETMASK, &old_mask, NULL);
+#    endif
 
         // return from runtime handler; continue processing the crash on the
         // signal thread until the worker takes over