As PC_FROM_UCONTEXT is never defined, GetPC() always returns nullptr:

Possible fix:

1. update

   glog/CMakeLists.txt

   Lines 215 to 233 in 6482757

   	set (_PC_FIELDS
   	"gregs[REG_PC]"
   	"gregs[REG_EIP]"
   	"gregs[REG_RIP]"
   	"sc_ip"
   	"uc_regs->gregs[PT_NIP]"
   	"gregs[R15]"
   	"arm_pc"
   	"mc_eip"
   	"mc_rip"
   	"__gregs[REG_EIP]"
   	"__gregs[REG_RIP]"
   	"ss.eip"
   	"__ss.__eip"
   	"ss.rip"
   	"__ss.__rip"
   	"ss.srr0"
   	"__ss.__srr0"
   	)

   by prefixing each entry with uc_mcontext./uc_mcontext-> (https://github.com/couchbase/gperftools/blob/846b775dfadb77901202ae7ddbac30ad1de7df01/m4/pc_from_ucontext.m4#L23-L43 seems to provide an up-to-date list of fields)
2. update try_compile () invocation.

   glog/CMakeLists.txt

   Lines 251 to 252 in 6482757

   	try_compile (HAVE_PC_FROM_UCONTEXT ${CMAKE_CURRENT_BINARY_DIR} ${_TMP}
   	COMPILE_DEFINITIONS _GNU_SOURCE=1)

   should say -D_GNU_SOURCE=1
3. set cache variable correctly (set (PC_FROM_UCONTEXT ${_PC_FIELD} CACHE STRING ""))
4. define the macro correctly (#cmakedefine PC_FROM_UCONTEXT ${PC_FROM_UCONTEXT})