CONFIG_UML_SOUND is not available for thedefaultarchitecture x86.
Result is shown for architecture um

Sound support

modulename: hostaudio.ko

configname: CONFIG_UML_SOUND

Linux Kernel Configuration
└─>UML Character Devices
└─>Sound support
In linux kernel since version 2.6.12  
This option enables UML sound support. If enabled, it will pull in
the UML hostaudio relay, which acts as a intermediary
between the host's dsp and mixer devices and the UML sound system.
It is safe to say 'Y' here.

source code: