How can you make a C compiler assume decimal literals (e.g. 1.23) are float and not double?

In my source code, if I write 1.23 as a literal, e.g. doThis(1.23), gcc assumes it's a double.

Rather than type doThis((float) 1.23), is there a way to use floats for decimal literals/constants unless otherwise specified in an individual source file?

Mega-bonus points, is there a way that works across (nearly) every C compiler?

Yes, the standard way is to write 1.23f. It works with every C compiler, since it is defined in ISO C99 section 6.4.4.2 Floating constants. ISO C90 and K&R have similar definitions.