Don't use -fno-strict-aliasing for optimized build

There doesn't seem to be any need for it, the library compiles fine without it
and the few warnings generated with -Wstrict-aliasing=2 are harmless (i.e. the
strict aliasing rule is not really broken).

configure

@@ -32915,7 +32915,7 @@ else
         fi
     else
         if test "$GCC" = yes ; then
-                                                OPTIMISE_CFLAGS="-O2 -fno-strict-aliasing"
+            OPTIMISE_CFLAGS="-O2"
         else
             OPTIMISE_CFLAGS="-O"
         fi

configure.in

@@ -5101,10 +5101,7 @@ else
         fi
     else
         if test "$GCC" = yes ; then
-            dnl Switch on optimisation but keep strict-aliasing off for
-            dnl now (see -fstrict-aliasing in the gcc manual). When it is
-            dnl switched back on consider using -Wstrict-aliasing=2.
-            OPTIMISE_CFLAGS="-O2 -fno-strict-aliasing"
+            OPTIMISE_CFLAGS="-O2"
         else
             OPTIMISE_CFLAGS="-O"
         fi