Always include target CPU architecture in About dialog Version Information

...not just for Windows.  This information is occasionally useful also on other
platforms that can run executables targeting different CPU architectures (like
Linux x86 and x86-64, or macOS Aarch64 and x86-64), e.g. when trying to track
down why a bug reporter's system doesn't find a JRE matching the architecture of
their LibreOffice installation.

For simplicity, use the existing _ARCH bootstrap variable, even if its values
differ from the hardcoded "x64" and "x86" that have been used here so far.

Change-Id: I76b40dd044397bf19e014d8a56d0314f455bc8ac
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/141768
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

cui/source/dialogs/about.cxx

@@ -17,9 +17,14 @@
  *   the License at http://www.apache.org/licenses/LICENSE-2.0 .
  */
 
+#include <sal/config.h>
+
+#include <cassert>
+
 #include <about.hxx>
 
 #include <osl/process.h>     //osl_getProcessLocale
+#include <rtl/bootstrap.hxx>
 #include <sal/log.hxx>       //SAL_WARN
 #include <vcl/settings.hxx>  //GetSettings
 #include <vcl/svapp.hxx>     //Application::
@@ -148,11 +153,10 @@ bool AboutDialog::IsStringValidGitHash(std::u16string_view hash) {
 OUString AboutDialog::GetVersionString() {
   OUString sVersion = CuiResId(TranslateId(nullptr, "%ABOUTBOXPRODUCTVERSION%ABOUTBOXPRODUCTVERSIONSUFFIX"));
 
-#ifdef _WIN64
-  sVersion += " (x64)";
-#elif defined(_WIN32)
-  sVersion += " (x86)";
-#endif
+  OUString arch;
+  auto const ok = rtl::Bootstrap::get("_ARCH", arch);
+  assert(ok); (void) ok;
+  sVersion += " (" + arch + ")";
 
 #if HAVE_FEATURE_COMMUNITY_FLAVOR
   sVersion += " / LibreOffice Community";