Fix compilation with --enable-gcc-warnings and -O1

Fix compilation with --enable-gcc-warnings and -O1
optimization level.
* configure.in: If --enable-gcc-warnings, disable
-Wunsafe-loop-optimizations for -O1 optimization level.
* src/doprnt.c (doprnt): Change type of tem to int, initialize
to avoid compiler warning.  Add eassert.
* src/search.c (simple_search): Initialize match_byte to avoid
compiler warning.  Add eassert.