Build is suddenly failing

Following the line below is the entire output of the compile/link showing the failure

Build target is mbed LPC1768.

Using mbed-os 5.10.1 library

The build has worked for literally years and as recently as a couple of days ago.  No major changes made recently.

The error message indicates that "__asm___23_NanostackRfPhyAtmel_cpp_b3c216a9___Z10delay_loopj "  is an undefined symbol.

And that the undefined symbol is referenced in source file "../../build/mbed-os/components/802.15.4_RF/atmel-rf-driver/source/NanostackRfPhyAtmel.cpp"

In the file-list section of Keil, "NanostackRfPhyAtmel.cpp" has an indication "problem in this file", 

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The entire output of the compile/link showing the failure

Build started

Using toolchain ARM_STD profile {'ENV': {'ARMLMD_LICENSE_FILE': '8224@10.100.182.21:8224@10.100.106.178'}, 'PATHS': {'ARMC6_PATH': '/opt/ARMCompiler6.15.13/bin/', 'ARM_PATH': '/opt/armcc5_06_u6/'}, 'common': ['-c', '--gnu', '-O3', '-Otime', '--split_sections', '--apcs=interwork'], 'cxx': ['--cpp', '--no_rtti'], 'COMPILE_C_AS_CPP': False, 'NEW_SCAN_RESOURCES': True}

scan /tmp/chroots/ch-4e3777d8-f0ef-41b1-92f9-235d3ee8f062/src

scan /tmp/chroots/ch-4e3777d8-f0ef-41b1-92f9-235d3ee8f062/extras/mbed-os.lib

Configuration error: 'static_memory_defines' is not defined. <-- Have always gotten this 

link irrig.LPC1768

Error: L6218E: Undefined symbol __asm___23_NanostackRfPhyAtmel_cpp_b3c216a9___Z10delay_loopj (referred from ../../build/mbed-os/components/802.15.4_RF/atmel-rf-driver/source/NanostackRfPhyAtmel.LPC1768.o).

Finished: 0 information, 0 warning and 1 error messages.

Error: L6218E: Undefined symbol __asm___23_NanostackRfPhyAtmel_cpp_b3c216a9___Z10delay_loopj (referred from ../../build/mbed-os/components/802.15.4_RF/atmel-rf-driver/source/NanostackRfPhyAtmel.LPC1768.o).

Finished: 0 information, 0 warning and 1 error messages.

Internal error.

Build failed

Build failed