Bug 1480590 - add support for aarch64 when setting up NSPR on Windows; r=chmanchester

config/external/nspr/pr/moz.build

@@ -93,8 +93,12 @@ elif CONFIG['OS_TARGET'] == 'WINNT':
       DEFINES['DO_NOT_WAIT_FOR_CONNECT_OVERLAPPED_OPERATIONS'] = True
     if CONFIG['CPU_ARCH'] == 'x86_64':
         DEFINES['_AMD64_'] = True
-    else:
+    elif CONFIG['CPU_ARCH'] == 'x86':
         DEFINES['_X86_'] = True
+    elif CONFIG['CPU_ARCH'] == 'aarch64':
+        DEFINES['_ARM64_'] = True
+    else:
+        error('Unsupported CPU_ARCH value: %s' % CONFIG['CPU_ARCH'])
 else:
     error('Not a supported OS_TARGET for NSPR in moz.build: "%s". Use --with-system-nspr' % CONFIG['OS_TARGET'])