Replace "if if " with "if " in comments

	* include/alloc_buffer.h: Replace "if if " with "if " in
	comments.
	* sysdeps/mips/memcpy.S: Likkewise.
	* sysdeps/mips/memset.S: Likewise.
	* sysdeps/x86_64/fpu/multiarch/svml_s_sincosf16_core_avx512.S:
	Likewise.
	* sysdeps/x86_64/fpu/multiarch/svml_s_sincosf4_core_sse4.S:
	Likewise.
	* sysdeps/x86_64/fpu/multiarch/svml_s_sincosf8_core_avx2.S:
	Likewise.