Explicitly disallow preprocessor #if

.github/pull_request_template.md

@@ -6,7 +6,7 @@
 #### Manually checked properties
 <!-- These checkboxes serve for the maintainers of PQClean to verify your submission. Please do not check them yourself. -->
 
-* [ ] `#ifdef`s only for header encapsulation
+* [ ] `#if`/`#ifdef`s only for header encapsulation
 * [ ] `api.h` does not include other files
 * [ ] No stringification macros
 * [ ] Output-parameter pointers in functions are on the left

README.md

@@ -65,7 +65,7 @@ _The checking of items on this list is still being developed. Checked items shou
 ## Requirements on C implementations that are manually checked
 
 * Minimalist Makefiles
-* `#ifdef`s only for header encapsulation
+* `#if`/`#ifdef`s only for header encapsulation
 * No stringification macros
 * Output-parameter pointers in functions are on the left
 * `const` arguments are labeled as `const`