This patch by Brian Paul.

--- XFree86-4.1.0/xc/lib/GL/glx/Imakefile~	Wed Jun 20 16:32:13 2001
+++ XFree86-4.1.0/xc/lib/GL/glx/Imakefile	Wed Jun 20 16:33:55 2001
@@ -87,7 +87,11 @@
 		vertarr.o \
 	        xfont.o
 
+#if defined(AlphaArchitecture)
+     GLX_DEFS = GlxDefines VidModeExtensionDefines -D__GLX_ALIGN64
+#else
      GLX_DEFS = GlxDefines VidModeExtensionDefines
+#endif
 
 #if BuildXF86DRI
      DRI_INCS = -I$(GLXLIBSRC)/dri