pgsql: Optimize pg_comp_crc32c_sse42 routine slightly, and also use it

Optimize pg_comp_crc32c_sse42 routine slightly, and also use it on x86.

Eliminate the separate 'len' variable from the loops, and also use the 4
byte instruction. This shaves off a few more cycles. Even though this
routine that uses the special SSE 4.2 instructions is much faster than a
generic routine, it's still a hot spot, so let's make it as fast as
possible.

Change the configure test to not test _mm_crc32_u64. That variant is only
available in the 64-bit x86-64 architecture, not in 32-bit x86. Modify
pg_comp_crc32c_sse42 so that it only uses _mm_crc32_u64 on x86-64. With
these changes, the SSE accelerated CRC-32C implementation can also be used
on 32-bit x86 systems.

This also fixes the 32-bit MSVC build.

Branch
------
master

Details
-------
http://git.postgresql.org/pg/commitdiff/936546dcbc24ad1f2b3d33e73aa5c5fde4d2be84

Modified Files
--------------
config/c-compiler.m4 | 10 +++++++---
configure | 12 ++++++------
src/port/pg_crc32c_sse42.c | 41 ++++++++++++++++++++++++++++-------------
3 files changed, 41 insertions(+), 22 deletions(-)