configure: check alsa/pulse support only for linux

- allows to build OSX without having to pass --without-alsa --without-pulse.
- update doc accordingly

Change-Id: I5b26c58d1954ef2d2613724c24fba750333ae890

README

@@ -106,7 +106,7 @@ make -j
 # Then the daemon
 cd ../../
 ./autogen.sh
-./configure --without-alsa --without-pulse --without-dbus --prefix=<install_path>
+./configure  --without-dbus --prefix=<install_path>
 make
 
 If you want to link against libringclient and native client easiest way is to

configure.ac

@@ -113,6 +113,7 @@ AS_IF([test "$SYS" = linux],[
       AC_MSG_RESULT([no])
     ])
 ])
+
 AM_CONDITIONAL(HAVE_ANDROID, test "${HAVE_ANDROID}" = "1")
 
 dnl override platform specific check for dependent libraries
@@ -264,7 +265,7 @@ if test "${HAVE_ANDROID}" = "1"; then
 fi
 AM_CONDITIONAL([BUILD_OPENSL], test "x$have_opensl" = "xyes")
 
-if test "${SYS}" != "mingw32"; then
+if test "${SYS}" = "linux"; then
 dnl Check for alsa development package - name: libasound2-dev
 ALSA_MIN_VERSION=1.0
 AC_ARG_WITH([alsa],
@@ -280,7 +281,7 @@ fi
 AM_CONDITIONAL(BUILD_ALSA, test "x$with_alsa" = "xyes")
 
 
-if test "${SYS}" != "mingw32"; then
+if test "${SYS}" = "linux"; then
 dnl Check for pulseaudio development package - name: libpulse-dev
 LIBPULSE_MIN_VERSION=0.9.15
 AC_ARG_WITH([pulse],