Due to post-build script not supporting custom board, both the below UART configurations are enabled on NuMaker-IoT-M2354 board:
-   UART0 PA7/PA6 enabled by bl2.bin
-   UART0 PB9/PB8 enabled by tfm_s.bin and later by mbed
Both PA7/PA6 and PB9/PB8 enabled on UART0, PB8 gets disturbed and stdin mis-behaves on NuMaker-IoT-M2354 board.

NuMaker-M2354       : UART TX/RX = UART0 PA7/PA6
NuMaker-IoT_M2354   : UART TX/RX = UART0 PB9/PB8

This bugfix tries to enable post-build for custom board to some degree (not completely), with Mbed CLI.
NOTE: For Mbed CLI, the build process still sees NuMaker-M2354's partition/ and applies its mcuboot build options. Custom board must align on these.