THRIFT-3288 c_glib: Build unit tests without compiler warnings

These changes allow the unit tests for C (GLib) to build without
compiler warnings, even with additional warnings enabled. They
include

- Disabling string-function optimizations when glibc is used, as
  these produce compiler warnings when a string function is used
  within a call to assert ();

- Remove the "LL" suffix (added in C99) from 64-bit integer
  literals;

- Replace C++-style ("//") comments with C-style equivalents;

- Remove unused constant declarations that generated warnings;
  and

- Mark (or remove, from main ()) unused function parameters.
diff --git a/lib/c_glib/test/testoptionalrequired.c b/lib/c_glib/test/testoptionalrequired.c
index 931d8be..ae0c3d2 100755
--- a/lib/c_glib/test/testoptionalrequired.c
+++ b/lib/c_glib/test/testoptionalrequired.c
@@ -74,7 +74,7 @@
   s2 = g_object_new (T_TEST_TYPE_SIMPLE, NULL);
   s3 = g_object_new (T_TEST_TYPE_SIMPLE, NULL);
 
-  // write-to-read with optional fields
+  /* write-to-read with optional fields */
   s1->im_optional = 10;
   assert (s1->__isset_im_default == FALSE);
   assert (s1->__isset_im_optional == FALSE);  
@@ -174,7 +174,7 @@
   t2 = g_object_new (T_TEST_TYPE_TRICKY2, NULL);
   t3 = g_object_new (T_TEST_TYPE_TRICKY3, NULL);
 
-  // throws protocol exception
+  /* throws protocol exception */
   write_to_read (THRIFT_STRUCT (t2), THRIFT_STRUCT (t3), NULL, &read_error);
   assert (read_error != NULL);
   g_error_free (read_error);