Refine format
Fix a bug - Keep global ABS as the Absolute symbol.
add Hexagon opcodes/encodings
Remove unused variables.
1. Explicitly sort symbols before emitting using new virtual method
GNULDBackend::orderSymbolTable().
2. Factor out code check whether a symbol has an entry in a .strtab to
the new virtual method GNULDBackend::hasEntryInStrTab().
3. Redefine orderSymbolTable() and hasEntryInStrTab() in the
MipsLDBackend class to satisfy MIPS ABI requirements.
4. Remove unnecessary redefined virtual methods MipsLDBackend::sizeNamePools()
and MipsLDBackend::emitDynNamePools().
Update golden files for MIPS tests.
Allow emulation to be specified more than once.
 1. add data structures to record alias in Module
 2. add interfaces in IRBuilder to export Module
 add alias support in ResolveInfo
weak alias support:
record alias in ELFReader when reading .so
weak alias support for x86 backend:
 output alias symbols when doing copy relocation.
code refinement.
Move Mips's mgot test case to Mips/mgot directory.
Enrich Mips android sysroot.
Add Mips abs32 testcase.
Fix a bug - We must add a CIE even the argumentation string is zero.

It looks like GNU ld refines the argumentation string if the string is zero length.
I will study this behavior and fix it later.
 code refinement:
   use vector instead of map to record aliases in Module.
This patch implements --defsym option.

1. Add --defsym symbol=expression option to the linker
2. Add test case for defsym.
3. Add postfix expression to evaluate expression
Enable x86 weak alias test
Add default FDE encoding to CIE with empty augmentation string