`gcc_except_table` and `eh_frame` segments

[AngheloAlf]

Two new segments to help disassembling C++ projects with exceptions enabled

This also add a new kind of label, the ehlabel (for error handling label). The actual name of the macro used can be changed with the asm_ehtable_label_macro option.

An example implementation of ehlabel:

.macro ehlabel label, visibility=global
.\visibility "\label"
"\label":
.endm

[ethteck]

@AngheloAlf other than promoting these to common segments, I think this is good to go

[AngheloAlf]

dun