Build failure after upgrade to Qt 5.12.0

Using  Xcode 10.14 (after reinstallation to latest version)

I installed Qt 5.12 and run into the following build errors

Running qtCreator with clang++ and qmake 

1)qmake :

xcrun: error: missing DEVELOPER_DIR path: /Applications/Xcode82.app/Contents/Developer/
~/Qt/5.12.0/clang_64/mkspecs/features/mac/sdk.mk:11: *** ^. Stop.

I could ignore this by commenting out :    #$(error ^)  in sdk.mk

2) Compile error with clang++

/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang++

fatal error: 'string.h' file not found

I could solve this by editing  ~/Qt/5.12.0/clang_64/mkspecs/qdevice.pri

and replaced QMAKE_MAC_SDK = macosx

with QMAKE_MAC_SDK = macosx10.14

Then everything builds fine.

I do not know what if the cause of this problem is Xcode of some settings in Qt.

Any help would be appreciated very much.

Kind regards Frans Meerhoff

PS We are very happy with Qt and QML