Fix SDK build issue due to updated arm-sdk

After a recent change to enable security flags:
d47f9a099a4ef992351237b0f2f562b5dc843397
compilation of the code in this repository with the arm-sdk results in
error messages from FORTIFY_SOURCE, which only compiles with
optimization levels 1 and 2.

Change the default build type to debugoptimized.

Reference changes:
    I910256c3aeffcbab0cbc33ced541b90576ce4151
    Ic1a91e58253fed283f67c44989fbc9126e18b7fe

Tested:
    SDK build with arm-sdk passes.
    Bitbake build passes.

Signed-off-by: Brandon Wyman <bjwyman@gmail.com>
Change-Id: I7eb1cdd23a8b4d8674de7d403b41114a44b8984c
diff --git a/meson.build b/meson.build
index 60b140f..4fb63d4 100644
--- a/meson.build
+++ b/meson.build
@@ -4,7 +4,8 @@
     default_options: [
         'warning_level=3',
         'werror=true',
-        'cpp_std=c++17'
+        'cpp_std=c++17',
+        'buildtype=debugoptimized'
     ],
     license: 'Apache-2.0',
     version: '1.0',