PTRACE ABI to read FXSAVE area for 32-bit inferior

Summary:
 - Problem occurs when:
    -- 32-bit inferiors run on x86_32 machine and
       the architecture doesn't have AVX feature

    -- This causes FPRType to be set to eFPRTypeFXSAVE

    -- PTRACE_GETFPREGS was being used to read FXSAVE area

    -- For 32-bit inferiors running on x86_32 machine,
       PTRACE_GETFPREGS reads FSAVE area and not FXSAVE area

 - Changed ptrace API to PTRACE_GETREGSET for 32-bit inferiors
    -- This reads FPR data in FXSAVE format.
    -- For 64-bit inferiors, no change has been made.

 - Modified XFAIL for TestReturnValue.py
    -- Earlier, this test was passing for Linux OS
    -- Now, it passes for Android OS as well

Change-Id: Ieed72bc969b79516fc7b263b32493aa1e7a1a2ac
Signed-off-by: Abhishek Aggarwal <abhishek.a.aggarwal@intel.com>

Reviewers: ovyalov, jingham, lldb-commits, tberghammer, labath

Subscribers: jevinskie, labath, tberghammer, danalbert

Differential Revision: http://reviews.llvm.org/D15042

llvm-svn: 254499