Fix ccall() returning a pointer in CAN_ADDRESS_2GB mode. (#25765)

`ccall()` returned pointers as negative numbers in CAN_ADDRESS_2GB
modes, breaking pointer `begin < end` comparisons.

Author: juj

src/lib/libccall.js

@@ -53,6 +53,8 @@ addToLibrary({
       }
 #if MEMORY64
       if (returnType === 'pointer') return Number(ret);
+#elif CAN_ADDRESS_2GB
+      if (returnType === 'pointer') return ret >>> 0;
 #endif
       if (returnType === 'boolean') return Boolean(ret);
       return ret;

test/core/test_ccall_return_pointer.c

@@ -0,0 +1,16 @@
+#include <emscripten.h>
+#include <stdio.h>
+
+int g_data;
+
+EMSCRIPTEN_KEEPALIVE void* getDataPtr() {
+  return &g_data;
+}
+
+int main() {
+  EM_ASM({
+    var ptr = ccall("getDataPtr", 'pointer');
+    assert(ptr > 0);
+  });
+  printf("ok\n");
+}

test/core/test_ccall_return_pointer.out

@@ -0,0 +1 @@
+ok

test/test_core.py

@@ -7173,6 +7173,12 @@ def test_ccall_cwrap_fast_path(self):
     self.set_setting('EXPORTED_FUNCTIONS', ['_print_bool'])
     self.do_runf('core/test_ccall.cpp', 'true')
 
+  @no_modularize_instance('ccall is not yet compatible with MODULARIZE=instance')
+  def test_ccall_return_pointer(self):
+    if self.get_setting('MINIMAL_RUNTIME'):
+      self.skipTest('ccall is not available in MINIMAL_RUNTIME')
+    self.do_core_test('test_ccall_return_pointer.c', cflags=['-sDEFAULT_LIBRARY_FUNCS_TO_INCLUDE=$ccall'])
+
   @no_modularize_instance('uses Module object directly')
   def test_EXPORTED_RUNTIME_METHODS(self):
     self.set_setting('DEFAULT_LIBRARY_FUNCS_TO_INCLUDE', ['$dynCall', '$ASSERTIONS'])