silence most warnings under macOS

For macOS Apple clang version 15.0.0 (clang-1500.3.9.4)
compiler, we have silenced the warnings that can be silenced.

We also updated `.gitignore` for `2014/maffiodo2` and `1995/vanschnitz`.

2012/tromp/Makefile

@@ -41,7 +41,7 @@ include ../../var.mk
 CSILENCE= -Wno-bitwise-op-parentheses -Wno-conditional-type-mismatch -Wno-error \
 	-Wno-implicit-function-declaration -Wno-incompatible-pointer-types \
 	-Wno-int-conversion -Wno-main -Wno-return-type -Wno-unused-parameter \
-	-Wno-deprecated-non-prototype
+	-Wno-deprecated-non-prototype -Wno-implicit-int
 
 # Common C compiler warning flags
 #