Partial undo, changes to ldelf.c retained.

Some platforms are still not working even with the integrated assembler disabled, will have to find another solution.

««« original CL description
cmd/cgo: disable clang's integrated assembler

Fixes #8348.

Clang's internal assembler (introduced by default in clang 3.4) understands the .arch directive, but doesn't change the default value of -march. This causes the build to fail when we use BLX (armv5 and above) when clang is compiled for the default armv4t architecture (which appears to be the default on all the distros I've used).

This is probably a clang bug, so work around it for the time being by disabling the integrated assembler when compiling the cgo assembly shim.

This CL also includes a small change to ldelf.c which was required as clang 3.4 and above generate more weird symtab entries.

LGTM=iant
R=golang-codereviews, iant
CC=golang-codereviews
https://golang.org/cl/156430044
»»»

LGTM=minux
R=iant, minux
CC=golang-codereviews
https://golang.org/cl/162880044