[RenderScript] Update the build rules for x86_64 support lib.

Bug: 19735423

  - Unlike other archs, x86_64 has both usr/lib and usr/lib64. we need
    to search for libm.so and libc.so in lib64/. Otherwise the linker
    will report error.

Change-Id: I2859bee066a9eb100828d90da8adf0f9817d77e6