cgo: implement bool/float/complex types

testdata/cgo/main.c

@@ -1,6 +1,13 @@
 #include "main.h"
 
 int global = 3;
+_Bool globalBool = 1;
+_Bool globalBool2 = 10; // test narrowing
+float globalFloat = 3.1;
+double globalDouble = 3.2;
+_Complex float globalComplexFloat = 4.1+3.3i;
+_Complex double globalComplexDouble = 4.2+3.4i;
+_Complex double globalComplexLongDouble = 4.3+3.5i;
 
 int fortytwo() {
 	return 42;