x86: enable PIE for dynamically linked executables

Compile all x86 programs on Android with -fPIE and -pie. This enables
PIE (Position Independent Executables), which helps protect Android
applications from exploitation due to memory management bugs.

Note 1: PIE *static* executables are not supported at this time and
require additional linker changes.

Note 2: This change compliments 026a85b1,
which was the exact same change, except for ARM.

Testing: Rebuilt the tree completely from scratch, and verified
that the system boots and basic functionality works in the emulator.

Change-Id: I990064c37da3d857e663b27f31fee05f689a2824