package/zynaddsubfx: fix alsa-lib handling

alsa-lib is optional, not mandatory, since the addition of the package
in commit 18a863063735e2c658fa6947a4e540e9dda6c431

Moreover, alsa support depends on BR2_PACKAGE_ALSA_LIB_SEQ (otherwise,
it is silently disabled)

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
(cherry picked from commit 2fc2191845799ae2358b752fa29839817d33ad82)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/zynaddsubfx/Config.in

@@ -2,8 +2,7 @@ config BR2_PACKAGE_ZYNADDSUBFX
 	bool "zynaddsubfx"
 	depends on BR2_INSTALL_LIBSTDCPP
 	depends on BR2_TOOLCHAIN_GCC_AT_LEAST_4_9 # C++11
-	depends on BR2_TOOLCHAIN_HAS_THREADS # alsa-lib, liblo
-	select BR2_PACKAGE_ALSA_LIB
+	depends on BR2_TOOLCHAIN_HAS_THREADS # liblo
 	select BR2_PACKAGE_FFTW
 	select BR2_PACKAGE_FFTW_SINGLE
 	select BR2_PACKAGE_LIBLO

package/zynaddsubfx/zynaddsubfx.mk

@@ -18,10 +18,16 @@ ZYNADDSUBFX_CONF_OPTS += -DOS_LIBRARIES=-latomic
 endif
 
 ZYNADDSUBFX_DEPENDENCIES = \
-	alsa-lib \
 	fftw-single \
 	liblo \
 	mxml \
 	zlib
 
+ifeq ($(BR2_PACKAGE_ALSA_LIB_SEQ),y)
+ZYNADDSUBFX_DEPENDENCIES += alsa-lib
+ZYNADDSUBFX_CONF_OPTS += -DAlsaEnable=ON
+else
+ZYNADDSUBFX_CONF_OPTS += -DAlsaEnable=OFF
+endif
+
 $(eval $(cmake-package))