When trying to run M-x Flymake-Mode in Emacs I get:
Flymake: Configuration error has occured while running (make -s -C ./CHK_SOURCES=helloworld_flymake.c SYNTAX_
Is this the actual content of your makefile? It looks like there is a space ' ' before the second line. This is supposed to be a tab:
helloworld: helloworld.c
gcc helloworld.c -o helloworld
More like this:
helloworld: helloworld.c
gcc helloworld.c -o helloworld
Keeping in mind, that the SO editor seems to have converted my tab character to spaces, so don't do that.
helloworld: helloworld.c
gcc helloworld.c -o helloworld