walloc | A small malloc implementation , for use in WebAssembly | Binary Executable Format library

You can use -o /dev/null to discard the output altogether, or you could send it to a temporary file which you then delete. If you're concerned with compile times, you can add -E in order to only run the preprocessor, which is the minimum in order for -H to work. That works because if you tell gcc to stop after preprocessing (-H), it doesn't matter if you also tell it to stop after creating an object file (-c). (That's an exception to the general rule that gcc uses the last of a set of conflicting options, which is designed to let you override options by adding to the end of a command-line.)

However, I can't help thinking that this is not really the best solution to your problem. It seems like you've hand-crafted a compiler invocation with a number of options, and then put it somewhere where it's difficult to modify. A better solution would be to use a makefile and set the value of the various standard makefile variables -- such as CFLAGS, CPPFLAGS, LDFLAGS, LDLIBS -- which are documented in the Gnu make manual. In simple cases, your Makefile might consist only of lines which set these variables, since Gnu make has built-in rules for common targets.