Add configure test to verify SSE2 code compiles.
Add configure test to verify SSE2 code compiles.

Make sure that emmintrin.h can be #include'd without causing a
compilation error, rather than blindly defining HAVE_SSE2 based on
architecture.  Attempts to force SSE2 compilation on a 32-bit Ubuntu
13.10 system running as a VMware guest resulted in a no-win choice
without any obvious explanation besides toolchain misconfiguration/bug:
- Suffer compilation failure due to __MMX__, __SSE__, and __SSE2__ not
  being defined, even if -mmmx, -msse, and -msse2 are manually
  specified (note that they appear to be enabled by default).
- Manually define __MMX__, __SSE__, and __SSE2__, and suffer compiler
  warnings that they are already automatically defined.  This results in
  successful compilation and execution, but the noise is intolerable.

shekkbuilder/jemalloc,sudosurootdev/external_jemalloc,wespelee/jemalloc,sudosurootdev/external_jemalloc,geekboxzone/lollipop_external_jemalloc,flyfeifan/jemalloc,dxq-git/jemalloc,Snaipe/jemalloc,Dmitry-Me/jemalloc,wfxiang08/jemalloc,TeamExodus/external_jemalloc,Dmitry-Me/jemalloc,vashstorm/jemalloc,ahmetmircik/jemalloc,vashstorm/jemalloc,CyanogenMod/android_external_jemalloc,VRToxin/android_external_jemalloc,CyanogenMod/android_external_jemalloc,Dmitry-Me/jemalloc,android-ia/platform_external_jemalloc,AndroidExternal/jemalloc,glandium/jemalloc,AndroidExternal/jemalloc,wqfish/jemalloc,8l/jemalloc,geekboxzone/mmallow_external_jemalloc,flyfeifan/jemalloc,shekkbuilder/jemalloc,awreece/jemalloc,CMRemix/android_external_jemalloc,lvfeng1130/jemalloc,garoose/jemalloc,CyanogenMod/android_external_jemalloc,lvfeng1130/jemalloc,TeamExodus/external_jemalloc,glandium/jemalloc,dxq-git/jemalloc,jemalloc/jemalloc-cmake,awreece/jemalloc,glandium/jemalloc,leebaok/jemalloc-4.2.1-readcode,tempbottle/jemalloc,flyfeifan/jemalloc,sudosurootdev/external_jemalloc,ahmetmircik/jemalloc,geekboxzone/lollipop_external_jemalloc,TeamExodus/external_jemalloc,lvfeng1130/jemalloc,yy-nm/jemalloc,ahmetmircik/jemalloc,vashstorm/jemalloc,shekkbuilder/jemalloc,tempbottle/jemalloc,flyfeifan/jemalloc,wqfish/jemalloc,VRToxin/android_external_jemalloc,android-ia/platform_external_jemalloc,CyanogenMod/android_external_jemalloc,xin3liang/platform_external_jemalloc,vashstorm/jemalloc,kmiku7/jemalloc,VRToxin/android_external_jemalloc,glandium/jemalloc,ahmetmircik/jemalloc,yy-nm/jemalloc,TeamExodus/external_jemalloc,AndroidExternal/jemalloc,Dmitry-Me/jemalloc,AndroidExternal/jemalloc,VRToxin/android_external_jemalloc,wqfish/jemalloc,wfxiang08/jemalloc,cpeterso/jemalloc,wespelee/jemalloc,shekkbuilder/jemalloc,leebaok/jemalloc-4.2.1-readcode,CMRemix/android_external_jemalloc,tempbottle/jemalloc,garoose/jemalloc,wfxiang08/jemalloc,lilothar/jemalloc,wfxiang08/jemalloc,cpeterso/jemalloc,wespelee/jemalloc,lilothar/jemalloc,tempbottle/jemalloc,CMRemix/android_external_jemalloc,cpeterso/jemalloc,cpeterso/jemalloc,android-ia/platform_external_jemalloc,geekboxzone/mmallow_external_jemalloc,xin3liang/platform_external_jemalloc,8l/jemalloc,jemalloc/jemalloc-cmake,xin3liang/platform_external_jemalloc,Snaipe/jemalloc,leebaok/jemalloc-4.2.1-readcode,geekboxzone/lollipop_external_jemalloc,geekboxzone/mmallow_external_jemalloc,android-ia/platform_external_jemalloc,lvfeng1130/jemalloc,awreece/jemalloc,dxq-git/jemalloc,kmiku7/jemalloc,kmiku7/jemalloc,wqfish/jemalloc,dxq-git/jemalloc,8l/jemalloc,garoose/jemalloc,geekboxzone/mmallow_external_jemalloc,kmiku7/jemalloc,jemalloc/jemalloc-cmake,awreece/jemalloc,lilothar/jemalloc,sudosurootdev/external_jemalloc,xin3liang/platform_external_jemalloc,yy-nm/jemalloc,yy-nm/jemalloc,CMRemix/android_external_jemalloc,Snaipe/jemalloc,wespelee/jemalloc,garoose/jemalloc,wqfish/jemalloc,Snaipe/jemalloc,jemalloc/jemalloc-cmake,geekboxzone/lollipop_external_jemalloc,leebaok/jemalloc-4.2.1-readcode,8l/jemalloc,lilothar/jemalloc