I'm compiling v8 based on rev a5fe3a0ac6392446044bedef67813f5899d8552c with clang version 5.0.0 (trunk 298539) and the following gn flags:

is_debug = true
v8_optimized_debug = false
is_component_build = true
symbol_level = 1

when debugging the resulting binaries, e.g. gdb --args out.gn/x64.debug/unittests I get errors like these:

warning: (Internal error: pc 0x7fcdf927e2cf in read in psymtab, but not in symtab.)

omitting symbol_level in my gn configuration makes the gdb errors go away