Add -W options from Makefile into meson warning_flags

Makefile options were more restrictive and produced more
warnings. This patch adds missing warning options into
meson build.

Makefile also has -Wall and -Wextra specified explicitly,
however this is covered by warning_level=2 which is already
set in meson.build. warning_level info:
https://github.com/mesonbuild/meson/issues/3275

There are few warning options that are present in meson,
but not in Makefile. These are left as is.

Tested: ninja test shows no warnings and tests pass

Change-Id: Id401bfd642dc3c13d85bd9a2dba56ada38714c25
Signed-off-by: Anastasia Klimchuk <aklm@chromium.org>
Original-Reviewed-on: https://review.coreboot.org/c/flashrom/+/58561
Original-Reviewed-by: Thomas Heijligen <src@posteo.de>
Reviewed-on: https://review.coreboot.org/c/flashrom-stable/+/72324
Reviewed-by: Nico Huber <nico.h@gmx.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
diff --git a/meson.build b/meson.build
index 1e571f5..2db7299 100644
--- a/meson.build
+++ b/meson.build
@@ -13,6 +13,8 @@
 
 # hide/enable some warnings
 warning_flags = [
+  '-Wshadow',
+  '-Wmissing-prototypes',
   '-Wwrite-strings',
   '-Wno-unused-parameter',
   '-Wno-address-of-packed-member',