Moved main function in its own CU to avoid symbol conflicts when calling other functions

Makefile.am

@@ -40,4 +40,5 @@ libcriterion_la_SOURCES = \
 	src/process.c \
 	src/process.h \
 	src/stats.c \
-	src/stats.h
+	src/stats.h \
+	src/main.c

src/main.c

@@ -0,0 +1,5 @@
+#include <criterion/criterion.h>
+
+int main(void) {
+    return criterion_run_all_tests();
+}

src/runner.c

@@ -164,7 +164,3 @@ int criterion_run_all_tests(void) {
 
     return strcmp("1", getenv("CRITERION_ALWAYS_SUCCEED") ?: "0") && res;
 }
-
-int main(void) {
-    return criterion_run_all_tests();
-}