Allow binding pre-loaded symbols in windows FFI.

Mimic the posix RTLD_NOW setting for dlopen by iterating
opened DLLs to look for symbols.

examples/ffi/so.c

@@ -2,22 +2,33 @@
 #include <stdint.h>
 #include <string.h>
 
+#ifdef _WIN32
+#define EXPORTER __declspec(dllexport) 
+#else
+#define EXPORTER
+#endif
+
+EXPORTER
 int int_fn(int a, int b) {
     return (a << 2) + b;
 }
 
+EXPORTER
 double my_fn(int64_t a, int64_t b, const char *x) {
     return (double)(a + b) + 0.5 + strlen(x);
 }
 
+EXPORTER
 double double_fn(double x, double y, double z) {
     return (x + y) * z * 3;
 }
 
+EXPORTER
 double double_many(double x, double y, double z, double w, double a, double b) {
     return x + y + z + w + a + b;
 }
 
+EXPORTER
 double double_lots(
     double a,
     double b,
@@ -32,6 +43,7 @@ double double_lots(
     return i + j;
 }
 
+EXPORTER
 double float_fn(float x, float y, float z) {
     return (x + y) * z;
 }
@@ -47,16 +59,19 @@ typedef struct {
     int c;
 } intintint;
 
+EXPORTER
 int intint_fn(double x, intint ii) {
     printf("double: %g\n", x);
     return ii.a + ii.b;
 }
 
+EXPORTER
 int intintint_fn(double x, intintint iii) {
     printf("double: %g\n", x);
     return iii.a + iii.b + iii.c;
 }
 
+EXPORTER
 intint return_struct(int i) {
     intint ret;
     ret.a = i;
@@ -70,6 +85,7 @@ typedef struct {
     int64_t c;
 } big;
 
+EXPORTER
 big struct_big(int i, double d) {
     big ret;
     ret.a = i;
@@ -78,10 +94,12 @@ big struct_big(int i, double d) {
     return ret;
 }
 
+EXPORTER
 void void_fn(void) {
     printf("void fn ran\n");
 }
 
+EXPORTER
 void void_ret_fn(int x) {
     printf("void fn ran: %d\n", x);
 }