C:\path\to\HX711_Arduino_Library\src\HX711.cpp:31:5: warning: this use of "defined" may not be portable [-Wexpansion-to-defined]
#if HAS_ATOMIC_BLOCK
^~~~~~~~~~~~~~~~
C:\path\to\HX711_Arduino_Library\src\HX711.cpp:31:5: warning: this use of "defined" may not be portable [-Wexpansion-to-defined]
C:\path\to\HX711_Arduino_Library\src\HX711.cpp:36:5: warning: this use of "defined" may not be portable [-Wexpansion-to-defined]
#if FAST_CPU
^~~~~~~~
C:\path\to\HX711_Arduino_Library\src\HX711.cpp:36:5: warning: this use of "defined" may not be portable [-Wexpansion-to-defined]
C:\path\to\HX711_Arduino_Library\src\HX711.cpp:36:5: warning: this use of "defined" may not be portable [-Wexpansion-to-defined]
C:\path\to\HX711_Arduino_Library\src\HX711.cpp:36:5: warning: this use of "defined" may not be portable [-Wexpansion-to-defined]
C:\path\to\HX711_Arduino_Library\src\HX711.cpp:36:5: warning: this use of "defined" may not be portable [-Wexpansion-to-defined]
C:\path\to\HX711_Arduino_Library\src\HX711.cpp:36:5: warning: this use of "defined" may not be portable [-Wexpansion-to-defined]
C:\path\to\HX711_Arduino_Library\src\HX711.cpp:130:6: warning: this use of "defined" may not be portable [-Wexpansion-to-defined]
#if HAS_ATOMIC_BLOCK
^~~~~~~~~~~~~~~~
C:\path\to\HX711_Arduino_Library\src\HX711.cpp:130:6: warning: this use of "defined" may not be portable [-Wexpansion-to-defined]
C:\path\to\HX711_Arduino_Library\src\HX711.cpp:133:8: warning: this use of "defined" may not be portable [-Wexpansion-to-defined]
#elif IS_FREE_RTOS
^~~~~~~~~~~~
C:\path\to\HX711_Arduino_Library\src\HX711.cpp:155:7: warning: this use of "defined" may not be portable [-Wexpansion-to-defined]
#if ARCH_ESPRESSIF
^~~~~~~~~~~~~~
C:\path\to\HX711_Arduino_Library\src\HX711.cpp:155:7: warning: this use of "defined" may not be portable [-Wexpansion-to-defined]
C:\path\to\HX711_Arduino_Library\src\HX711.cpp:159:7: warning: this use of "defined" may not be portable [-Wexpansion-to-defined]
#if ARCH_ESPRESSIF
^~~~~~~~~~~~~~
C:\path\to\HX711_Arduino_Library\src\HX711.cpp:159:7: warning: this use of "defined" may not be portable [-Wexpansion-to-defined]
C:\path\to\HX711_Arduino_Library\src\HX711.cpp:164:6: warning: this use of "defined" may not be portable [-Wexpansion-to-defined]
#if IS_FREE_RTOS
^~~~~~~~~~~~
When building with warnings enabled:
I think it's complaining that your are trying to use the value of a #define in an #if, which may not be portable. See https://stackoverflow.com/questions/42074035/how-to-deal-with-clangs-3-9-wexpansion-to-defined-warning