Revert "Fix use of symbols in literals"

This seems to be unnecessary with current setups and actively breaks
things on arm without --enable-pic.

This reverts commit 76a72f00e0af8b8bacb4417e6806561d4c596dcc.
support probing of assembler type/version with -v or --version

When no input file was found but the compiler command contains -v or
--version just execute the command. Used by Libav's configure to
probe type and version of the backing assembler.
add separate options for gas-preprocessor

Options for gas-preprocessor need to be separated with ' -- ' from the
assembler command line.
The target architecture can now be set explicitly with the added '-arch'
option.
aarch64: handle ldr = pseudo instruction
Add as-type option

Allows differating between assemblers and will allow using
gas-preprocessor on linux.
linux: use as-type to make the output suitable for gas/clang on linux

Tested with libav's fate using gas on armv7 and clang-3.4 on aarch64.