Automerge: [libc] Fix -Wshorten-64-to-32 in fileop_test. (#168451)

Explicitly cast 0 to size_t type to match fread() return type. This
follows the pattern used elsewhere in this file, and fixes
-Wshorten-64-to-32 warnings when building the test.

Author: vonosmas

libc/test/src/stdio/fileop_test.cpp

@@ -101,7 +101,7 @@ TEST_F(LlvmLibcFILETest, SimpleFileOperations) {
 
   // This is not a readable file.
   ASSERT_THAT(LIBC_NAMESPACE::fread(data, 1, 1, file),
-              returns(EQ(0)).with_errno(NE(0)));
+              returns(EQ(size_t(0))).with_errno(NE(0)));
 
   ASSERT_EQ(0, LIBC_NAMESPACE::fclose(file));
 
@@ -175,7 +175,7 @@ TEST_F(LlvmLibcFILETest, FOpenFWriteSizeGreaterThanOne) {
   // Trying to read more should fetch nothing.
   ASSERT_THAT(
       LIBC_NAMESPACE::fread(read_data, sizeof(MyStruct), WRITE_NMEMB, file),
-      returns(EQ(0)).with_errno(EQ(0)));
+      returns(EQ(size_t(0))).with_errno(EQ(0)));
   EXPECT_NE(LIBC_NAMESPACE::feof(file), 0);
   EXPECT_EQ(LIBC_NAMESPACE::ferror(file), 0);
   ASSERT_EQ(LIBC_NAMESPACE::fclose(file), 0);