CONFIG_PPC_LIB_RHEAP is not available for thedefaultarchitecture x86.
Result is shown for architecture powerpc

CONFIG_PPC_LIB_RHEAP (not configurable)

modulename: rheap.ko

configname: CONFIG_PPC_LIB_RHEAP

Linux Kernel Configuration
└─>PPC_LIB_RHEAP
In linux kernel since version 2.6.24 (release Date: 2008-01-24)  
source code:
arch/powerpc/lib/rheap.c