Fix player movement in negative directions

Watcom defaults to unsigned char, but codebase assumes char to be signed.
In player input struct speed is stored as char (1 byte) that needs to be signed.

Co-authored-by: kmeaw <[email protected]>

src/CMakeLists.txt

@@ -96,6 +96,7 @@ set_target_properties(rusdoom PROPERTIES
 target_compile_options(rusdoom PRIVATE
     -wx
     -wcd=303
+    -j # treat char as signed
 )
 
 install(TARGETS rusdoom RUNTIME