Crank up the compiler warnings

`-Weverything` doesn't usually get used because `ruby.h` doesn't
compile with it as of 2.2.2.

Author: tamird

ext/mysql2/extconf.rb

@@ -98,11 +98,21 @@ def asplode lib
   asplode h unless have_header h
 end
 
-# These gcc style flags are also supported by clang and xcode compilers,
-# so we'll use a does-it-work test instead of an is-it-gcc test.
-gcc_flags = ' -Wall -funroll-loops'
-if try_link('int main() {return 0;}', gcc_flags)
-  $CFLAGS << gcc_flags
+# This is our wishlist. We use whichever flags work on the host.
+# -Wall and -Wextra are included by default.
+%w(
+  -Werror
+  -Weverything
+  -fsanitize=address
+  -fsanitize=integer
+  -fsanitize=thread
+  -fsanitize=memory
+  -fsanitize=undefined
+  -fsanitize=cfi
+).each do |flag|
+  if try_link('int main() {return 0;}', flag)
+    $CFLAGS << ' ' << flag
+  end
 end
 
 if RUBY_PLATFORM =~ /mswin|mingw/

ext/mysql2/result.c

@@ -59,7 +59,7 @@ typedef struct {
   int streaming;
   ID db_timezone;
   ID app_timezone;
-  int block_given;
+  VALUE block_given;
 } result_each_args;
 
 VALUE cBigDecimal, cDateTime, cDate;
@@ -346,8 +346,7 @@ static VALUE rb_mysql_result_fetch_row_stmt(VALUE self, MYSQL_FIELD * fields, co
   }
 
   {
-    int r = (int)rb_thread_call_without_gvl(nogvl_stmt_fetch, wrapper->stmt, RUBY_UBF_IO, 0);
-    switch(r) {
+    switch((uintptr_t)rb_thread_call_without_gvl(nogvl_stmt_fetch, wrapper->stmt, RUBY_UBF_IO, 0)) {
       case 0:
         /* success */
         break;