flags.txt

-mcpu=cortex-m4 -mthumb -mno-thumb-interwork -DTHUMB_NO_INTERWORKING -DTHUMB_PRESENT -g -Os -mlittle-endian  -mfloat-abi=hard -mfpu=fpv4-sp-d16 -fsingle-precision-constant -fcheck-new -std=c++11 -fno-rtti -fno-exceptions -fno-non-call-exceptions -fstack-usage -fno-threadsafe-statics -W -Wall -Wextra -Wdouble-promotion -DSTM32F401xC -DCORTEX_USE_FPU=TRUE -DARM_MATH_CM4 -D__FPU_PRESENT

Compiler Explorer
-mcpu=cortex-m4 -Ofast -mlittle-endian -mfloat-abi=hard -mfpu=fpv4-sp-d16 -fsingle-precision-constant -fcheck-new -std=c++11 -fno-rtti -fno-exceptions -fno-non-call-exceptions -fstack-usage -fno-threadsafe-statics -W -Wall -Wextra -Wdouble-promotion -DSTM32F401xC -DCORTEX_USE_FPU=TRUE -DARM_MATH_CM4 -D__FPU_PRESENT

link
-mcpu=cortex-m4 -mthumb -mno-thumb-interwork -DTHUMB_NO_INTERWORKING -DTHUMB_PRESENT -g -Os -mlittle-endian  -mfloat-abi=hard -mfpu=fpv4-sp-d16 -fsingle-precision-constant -fcheck-new -nostartfiles

( -fno-threadsafe-statics)