Added support for two more (bfd) linker flags that will be useful

Added support for two more (bfd) linker flags that will be useful
to counter the somewhat conservative handling of intrinsics by pnacl.
For example: when we see a use of the sin() function we will typically link
in a copy of sin() using floating point emulation even if the llc backend
can generate a corresponding cpu/copro instructions for sin.
This bloats pnacl binaries sowewhat.
The -gc-sections instructs the linker to throw out unused functions such as
 sin(). This only works if they reside in their own section which can be achieved with the -ffunction-section (llvm-)gcc option or via manual annotation.
NOTE: this option increases link time somewhat
Committed: http://src.chromium.org/viewvc/native_client?view=rev&revision=5808

[robertm, 2011-06-27 17:04:04]

PTAL

[jvoung - send to chromium..., 2011-06-27 17:12:54]

http://codereview.chromium.org/7273005/diff/1/tools/llvm/driver/pnacl-ld.py
File tools/llvm/driver/pnacl-ld.py (right):

http://codereview.chromium.org/7273005/diff/1/tools/llvm/driver/pnacl-ld.py#n...
tools/llvm/driver/pnacl-ld.py:154: ( '(--print-gc-sections)',     
"env.append('LD_BFD_FLAGS', $0)"),
Should be okay to have it be LD_FLAGS, at least, it is also available in gold.

[robertm, 2011-06-27 17:31:16]

PTAL

http://codereview.chromium.org/7273005/diff/1/tools/llvm/driver/pnacl-ld.py
File tools/llvm/driver/pnacl-ld.py (right):

http://codereview.chromium.org/7273005/diff/1/tools/llvm/driver/pnacl-ld.py#n...
tools/llvm/driver/pnacl-ld.py:154: ( '(--print-gc-sections)',     
"env.append('LD_BFD_FLAGS', $0)"),
On 2011/06/27 17:12:54, jvoung wrote:
> Should be okay to have it be LD_FLAGS, at least, it is also available in gold.

Done.

[jvoung - send to chromium..., 2011-06-27 18:17:01]

LGTM