build: Fix missing void parameters in C

Add missing void parameters to several functions. This prepares the code
to apply the -Wstrict-prototypes warning.

Bug: 329
Change-Id: Id5b152e9f8d77d07e99a6e781b3a3c4ef9bd08c0
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/35560
Commit-Queue: Wyatt Hepler <hepler@google.com>
Reviewed-by: Ewout van Bekkum <ewout@google.com>
diff --git a/pw_assert/assert_backend_compile_test_c.c b/pw_assert/assert_backend_compile_test_c.c
index c602f37..a4aaced 100644
--- a/pw_assert/assert_backend_compile_test_c.c
+++ b/pw_assert/assert_backend_compile_test_c.c
@@ -25,7 +25,7 @@
 
 #include "pw_assert/assert.h"
 
-static void EnsureNullIsIncluded() {
+static void EnsureNullIsIncluded(void) {
   // This is a compile check to ensure NULL is defined. It comes before the
   // status.h include to ensure we don't accidentally get NULL from status.h.
   PW_CHECK_NOTNULL(0xa);
@@ -64,7 +64,7 @@
 
 static int Add3(int a, int b, int c) { return a + b + c; }
 
-void AssertBackendCompileTestsInC() {
+void AssertBackendCompileTestsInC(void) {
   {  // TEST(Crash, WithAndWithoutMessageArguments)
     MAYBE_SKIP_TEST;
     PW_CRASH(FAIL_IF_HIDDEN);