Fix typo in macro and add missing static_cast for WASM builds.

Corrects `__asjms__` to `__asmjs__` and adds a `static_cast<size_t>` to the result of `getpagesize() - 1`.

Without this static cast, emscripten based builds will trigger `-Wsign-conversion` on this line.

PiperOrigin-RevId: 827655583
Change-Id: I19b8ed7d3240409127934ac6debcb523fdb73e22

Author: Abseil Team

absl/debugging/failure_signal_handler.cc

@@ -157,8 +157,8 @@ const char* FailureSignalToString(int signo) {
 #ifdef ABSL_HAVE_SIGALTSTACK
 
 static bool SetupAlternateStackOnce() {
-#if defined(__wasm__) || defined(__asjms__)
-  const size_t page_mask = getpagesize() - 1;
+#if defined(__wasm__) || defined(__asmjs__)
+  const size_t page_mask = static_cast<size_t>(getpagesize()) - 1;
 #else
   const size_t page_mask = static_cast<size_t>(sysconf(_SC_PAGESIZE)) - 1;
 #endif