Exclude -Wmisleading-indentation when -save-temps

That option may be triggered wrongly by pre-processed files.

configure.ac

@@ -682,6 +682,10 @@ AS_CASE(["$GCC:${warnflags+set}:${extra_warnflags:+set}:"],
     AS_IF([test $gcc_major -le 6], [
 	extra_warnflags="$extra_warnflags -Wno-maybe-uninitialized"
     ])
+    AS_CASE([ $CFLAGS ], [*" -save-temps="*|*" -save-temps "*], [], [
+	extra_warnflags="$extra_warnflags -Werror=misleading-indentation"
+    ])
+
     # ICC doesn't support -Werror=
     AS_IF([test $icc_version -gt 0], [
 	particular_werror_flags=no
@@ -693,7 +697,6 @@ AS_CASE(["$GCC:${warnflags+set}:${extra_warnflags:+set}:"],
 		 -Werror=duplicated-cond \
 		 -Werror=implicit-function-declaration \
 		 -Werror=implicit-int \
-		 -Werror=misleading-indentation \
 		 -Werror=pointer-arith \
 		 -Werror=shorten-64-to-32 \
 		 -Werror=write-strings \