[libc] remove use after free in tests.

There were some tests added that attempted to access files after they
were closed to test errno behavior, this caused sanitizer issues. Those
portions of the tests have been disabled.

Differential Revision: https://reviews.llvm.org/D139878

Author: michaelrj-google

libc/test/src/stdio/fileop_test.cpp

@@ -114,18 +114,18 @@ TEST(LlvmLibcFILETest, SimpleFileOperations) {
 
   // Check that the other functions correctly set errno.
 
-  errno = 0;
-  ASSERT_NE(__llvm_libc::fseek(file, 0, SEEK_SET), 0);
-  EXPECT_NE(errno, 0);
-
-  errno = 0;
-  ASSERT_NE(__llvm_libc::fclose(file), 0);
-  EXPECT_NE(errno, 0);
-
-  errno = 0;
-  ASSERT_EQ(__llvm_libc::fopen("INVALID FILE NAME", "r"),
-            static_cast<FILE *>(nullptr));
-  EXPECT_NE(errno, 0);
+  // errno = 0;
+  // ASSERT_NE(__llvm_libc::fseek(file, 0, SEEK_SET), 0);
+  // EXPECT_NE(errno, 0);
+
+  // errno = 0;
+  // ASSERT_NE(__llvm_libc::fclose(file), 0);
+  // EXPECT_NE(errno, 0);
+
+  // errno = 0;
+  // ASSERT_EQ(__llvm_libc::fopen("INVALID FILE NAME", "r"),
+  //           static_cast<FILE *>(nullptr));
+  // EXPECT_NE(errno, 0);
 }
 
 TEST(LlvmLibcFILETest, FFlush) {

libc/test/src/stdio/ftell_test.cpp

@@ -55,9 +55,9 @@ class LlvmLibcFTellTest : public __llvm_libc::testing::Test {
 
     ASSERT_EQ(0, __llvm_libc::fclose(file));
 
-    errno = 0;
-    ASSERT_EQ(__llvm_libc::ftell(file), long(-1));
-    ASSERT_NE(errno, 0);
+    // errno = 0;
+    // ASSERT_EQ(__llvm_libc::ftell(file), long(-1));
+    // ASSERT_NE(errno, 0);
   }
 };