Only add strip option '-s' for linker flags

Fixes some build warnings with clang.
ppc: fix build on certain PowerPC variants without Altivec
arm: implement x264_predict_4x4_v_armv6

Alone probably not worth it but allows use of predict_4x4_dc|h_armv6
in intra_sad|satd_x3_4x4_neon.
arm: add missing macro instantiation for x264_pixel_avg_4x16_neon

checkasm --bench on a cortex-a9:
avg_4x16_c: 8910
avg_4x16_neon: 2091
arm: implement deblock_strength_neon

Based on deblock_strength_avx.

checkasm --bench on a cortex-a9:
deblock_strength_c: 14611
deblock_strength_neon: 1848
arm: x264_plane_copy_deinterleave_neon

plane_copy_deinterleave_c: 42988
plane_copy_deinterleave_neon: 10184
arm: load_deinterleave_chroma_f{dec,enc}_neon

load_deinterleave_chroma_fdec_c: 4055
load_deinterleave_chroma_fdec_neon: 995
load_deinterleave_chroma_fenc_c: 4071
load_deinterleave_chroma_fenc_neon: 992
arm: x264_plane_copy_deinterleave_rgb_neon

plane_copy_deinterleave_rgb_c: 31543
plane_copy_deinterleave_rgb_neon: 8312
arm: x264_plane_copy_interleave_neon

plane_copy_interleave_c: 40285
plane_copy_interleave_neon: 10137
arm: x264_store_interleave_chroma_neon

store_interleave_chroma_c: 4036
store_interleave_chroma_neon: 1043
arm: x264_coeff_last8_arm

checkasm --bench on a coretex-a9:
coeff_last8_c: 173
coeff_last8_armv6: 151

60 instead of 73 cycles in ~130k runs on the same cpu while encoding.
aarch64: require PIC in shared mode
arm: move all .macro/.endm to column 0
arm: do not export every asm function

Based on Libav's libavutil/arm/asm.S. Also prevents having the same
label twice for every function on systems not defining EXTERN_ASM.
Clang's integrated assembler does not like it.
arm: correct x264_mc_chroma_neon function declaration
arm: use the weight_fn_t typedef for mc weight function arrays
x86: add missing initializations for high bit-depth variance
x86: add missing initialization for high bit-depth sa8d_satd
x86util: XOP optimized HADDD
x86: XOP pixel_ssd_nv12_core