Add flag to enable Dwarf exception handling on ARM

Add flag to enable Dwarf exception handling on ARM

Previously EABI EH was disabled for NaCl but not explicitly disabled for
Non-SFI mode. Some changes upstream for better ARM EHABI support caused
EHABI unwind info to be unconditionally emitted (into the .ARM.exidx section)
which has references to aeabi_ functions which we do not include in our
compiler-rt.
Introduce a flag to fully disable EHABI support for ARM (to be used by
Non-SFI mode) and clean up the disabling of EHABI for SFI mode as well.

R=jfb@chromium.org, mseaborn@chromium.org
BUG= https://code.google.com/p/nativeclient/issues/detail?id=3930

Committed: https://gerrit.chromium.org/gerrit/gitweb?p=native_client/pnacl-llvm.git;a=commit;h=a9072baedea1fd8759ab9bd0ed0c0e2821bdba7c

[Derek Schuff, 2014-11-19 18:51:30]

This patch is against the 3.5 branch. The driver will use the
-arm-enable-dwarf-eh flag in addition to -arm-enable-aeabi-functions=0

[JF, 2014-11-19 19:32:05]

https://codereview.chromium.org/738143002/diff/1/lib/Target/ARM/ARMSubtarget.h
File lib/Target/ARM/ARMSubtarget.h (right):

https://codereview.chromium.org/738143002/diff/1/lib/Target/ARM/ARMSubtarget....
lib/Target/ARM/ARMSubtarget.h:388: !isTargetDarwin() && !isTargetWindows() &&
!EnableARMDwarfEH;//@LOCALMOD
!isTargetNaCl() ?

[Derek Schuff, 2014-11-19 19:56:48]

https://codereview.chromium.org/738143002/diff/1/lib/Target/ARM/ARMSubtarget.h
File lib/Target/ARM/ARMSubtarget.h (right):

https://codereview.chromium.org/738143002/diff/1/lib/Target/ARM/ARMSubtarget....
lib/Target/ARM/ARMSubtarget.h:388: !isTargetDarwin() && !isTargetWindows() &&
!EnableARMDwarfEH;//@LOCALMOD
On 2014/11/19 19:32:05, JF wrote:
> !isTargetNaCl() ?
isTargetNaCl doesn't work for Non-SFI mode, which uses the Linux OS.

but !isTargetNaCl shoud probably be included for SFI NaCl though.

[JF, 2014-11-20 18:42:18]

lgtm

[Derek Schuff, 2014-11-20 19:32:47]

Committed patchset #2 (id:20001) manually as
a9072baedea1fd8759ab9bd0ed0c0e2821bdba7c (presubmit successful).