build: don't disable the aliasing checks

We now don't break the strict aliasing rules.

Also, having a compiler flag that disables a warning among the flags that are
meant to add extra sanity checking is not correct either:
--enable-extra-warnings=no would generate a bad aliasin warning while
the --enable-extra-warnings=yes would not.

m4/compiler_warnings.m4

@@ -10,7 +10,7 @@ if test "$GCC" = "yes" -a "$set_more_warnings" != "no"; then
 	for option in -Wmissing-declarations -Wmissing-prototypes \
 		      -Wdeclaration-after-statement -Wstrict-prototypes \
 		      -Wno-unused-parameter -Wno-sign-compare \
-		      -fno-strict-aliasing -Wno-deprecated-declarations \
+		      -Wno-deprecated-declarations \
 		      -Wno-unused-but-set-variable -Wformat-security; do
 		SAVE_CFLAGS="$CFLAGS"
 		CFLAGS="$CFLAGS $option"