SUMMARY
Kdevelop 5.3.0 (and possibly 5.2.4) fails to build duchain information for a C/C++ CMake project when option -march=armv7e-m is added in add_definition() in CMakeLists.txt. I have installed necessary ARM gcc compiler, so that the code compiles fine.

STEPS TO REPRODUCE
1. Create a CMake C/C++ project for ARM compilation with necessary overrides for CMAKE_C_COMPILER, etc.
2. Add definition -march=armv7e-m using add_definition()
3. Open/Import this project in KDevelop v5.3.0

OBSERVED RESULT
All code text appears without syntax highlighting, and mostly black text, like in plain text editor (not even like in vim or Kate). Navigation, Outline, etc. do not work.

EXPECTED RESULT
Syntax highlighting should work fine along with other normal features of the CLang support.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: KDE Neon 5.14.4
(available in About System)
KDE Plasma Version: 5.14.4
KDE Frameworks Version: 5.52.0
Qt Version: 5.11.2

ADDITIONAL INFORMATION
The workaround for this is use -mcpu=cortex-m4 or a specific CPU of interest and not to set -march=armv7e-m

When KDevelop is run with KDEV_CLANG_DISPLAY_ARGS=1 environment variable, the command line of clang is shown. When that command is run on terminal, you see an error that 

error: unknown target CPU 'armv7e-m'

thrown by clang.

This is perhaps the root cause of the issue. The workaround suggested above actually works because clang ignores -mcpu=... argument, but gcc does not.

It would be good if someone can look into a way to make march setting work because for all practical reasons C or C++ syntax is not dependent on the architecture.