libatomic.a contains relocs unknown to old android linker

[cjhopman]

Android linker <5.0 does not understand R_386_IRELATIVE. The gcc toolchain will use this for functions with ifunc attribute.

The ndk's libatomic uses the ifunc attribute and thus this relocation. Code like the following:

uint64_t a = 0, b = 0;
__atomic_store(&a, &b, __ATOMIC_SEQ_CST);

compiled w/ clang will fail to load on android <5.0 with error like:
java.lang.UnsatisfiedLinkError: dlopen failed: unknown reloc type 42 @ 0xa869f454 (75)

[DanAlbert]

Dup of #31