Tests: Fix -Wstrict-prototypes warnings in some C sources

Some RunCMake tests fail with this warning due to extra stderr content:

    warning: this old-style function definition is not preceded by a prototype

Convert `foo()` to `foo(void)` in `.c` sources of affected tests.

1 files changed, 1 insertions, 1 deletions

diff --git a/Tests/RunCMake/PrecompileHeaders/empty.c b/Tests/RunCMake/PrecompileHeaders/empty.c
index 30ae1c4..2a51ebc 100644
--- a/Tests/RunCMake/PrecompileHeaders/empty.c
+++ b/Tests/RunCMake/PrecompileHeaders/empty.c
@@ -1,3 +1,3 @@
-void nothing()
+void nothing(void)
 {
 }