Due to the way in which the configure script silently falls back to a non-SIMD build...

Due to the way in which the configure script silently falls back to a non-SIMD build if SIMD can't be enabled, we accidentally released iOS ARM v7 and v7s binaries in 1.3.0 that did not contain NEON SIMD code, because gas-preprocessor.pl wasn't in the PATH.  In order to prevent this from happening again, specifying --with-simd now has the effect of forcing a SIMD build, and if this argument is specified, any issues encountered while enabling SIMD are treated as fatal.

git-svn-id: svn+ssh://svn.code.sf.net/p/libjpeg-turbo/code/branches/1.3.x@1039 632fc199-4ca6-4c93-a231-07263d6284db