Implicit int error when using with Clang

[jakurzak]

When configuring using amdclang on OLCF machines, I get:

configure: flink.c:1:1: error: type specifier missing, defaults to 'int'; ISO C99 and later do not support implicit int [-Wimplicit-int]
main(){ FF(); return 0; }
^
int
flink.c:1:9: error: call to undeclared function 'f_fun'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
main(){ FF(); return 0; }
        ^
<command line>:1:12: note: expanded from here
#define FF f_fun
           ^
2 errors generated.
configure: error: giving up

which can be remedied by changing

echo "main(){ FF(); return 0; }" > flink.c

to

echo "int main(){ int FF(); return 0; }" > flink.c

in configure and configure.ac

Any reason not to?