Fixed use of alloca() in libspeex on Solaris, I think.

Fixes Bugzilla #3938.

code/libspeex/config.h

@@ -6,6 +6,9 @@
 // SSE is enabled.
 #ifndef _USE_SSE
 #  define USE_ALLOCA
+#  if defined(__sun)  /* Solaris needs this for alloca(). */
+#    define HAVE_ALLOCA_H
+#  endif
 #endif
 
 /* Default to floating point */