RFR: 8014231: --with-alsa configuration options don't add include or lib directories to proper flags

[Erik Joelsson]

The ALSA_LIBS and ALSA_CFLAGS variable were correctly setup in 
configure, but never got propagated any further. This patch adds them to 
spec.gmk.in to make them available to make, and to the compilation of 
libjsoundalsa.

http://cr.openjdk.java.net/~erikj/8014231/webrev.01/

/Erik