how to create a library compatible with the GNU toolchain

I have a Keil MDK project which outputs a library mc_comms.lib.  I have another Keil project which uses this library and don't have any issues. My customer is using STM Cube and can't build the same test project with the same library.

c:\st\stm32cubeide_1.6.0\stm32cubeide\plugins\com.st.stm32cube.ide.mcu.externaltools.gnu-tools-for-stm32.9-2020-q2-update.win32_1.5.0.202011040924\tools\arm-none-eabi\bin\ld.exe: cannot find -lB:/STM32/G4/Examples/CubeIDE_1_6_0/zti_lib/zti_lib/lib/mc_comms.lib
FYI:  

b:\STM32\G4\Examples\CubeIDE_1_6_0\zti_lib\zti_lib\lib>dir
Volume in drive B is home
Volume Serial Number is 4D4B-F115

Directory of b:\STM32\G4\Examples\CubeIDE_1_6_0\zti_lib\zti_lib\lib

03/18/2021 11:34 <DIR> .
03/17/2021 20:14 <DIR> ..
03/17/2021 18:16 2,139 mc_comms.h
03/18/2021 11:33 32,674 mc_comms.lib
2 File(s) 34,813 bytes
2 Dir(s) 11,366,381,383,680 bytes free

b:\STM32\G4\Examples\CubeIDE_1_6_0\zti_lib\zti_lib\lib>

Even if I change to GNU toolchain I still have issues: 

linking...
c:\st\stm32cubeide_1.6.0\stm32cubeide\plugins\com.st.stm32cube.ide.mcu.externaltools.gnu-tools-for-stm32.9-2020-q2-update.win32_1.5.0.202011040924\tools\arm-none-eabi\bin\ld.exe: c:/st/stm32cubeide_1.6.0/stm32cubeide/plugins/com.st.stm32cube.ide.mcu.externaltools.gnu-tools-for-stm32.9-2020-q2-update.win32_1.5.0.202011040924/tools/bin/../lib/gcc/arm-none-eabi/9.3.1/../../../../arm-none-eabi/lib/thumb/v7e-m+fp/hard\libc.a(lib_a-exit.o): in function `exit':
exit.c:(.text.exit+0x16): undefined reference to `_exit'
c:\st\stm32cubeide_1.6.0\stm32cubeide\plugins\com.st.stm32cube.ide.mcu.externaltools.gnu-tools-for-stm32.9-2020-q2-update.win32_1.5.0.202011040924\tools\arm-none-eabi\bin\ld.exe: ./out/startup_stm32g431xx.o:(.text+0x0): undefined reference to `_sidata'
c:\st\stm32cubeide_1.6.0\stm32cubeide\plugins\com.st.stm32cube.ide.mcu.externaltools.gnu-tools-for-stm32.9-2020-q2-update.win32_1.5.0.202011040924\tools\arm-none-eabi\bin\ld.exe: ./out/startup_stm32g431xx.o:(.text+0x4): undefined reference to `_sdata'
c:\st\stm32cubeide_1.6.0\stm32cubeide\plugins\com.st.stm32cube.ide.mcu.externaltools.gnu-tools-for-stm32.9-2020-q2-update.win32_1.5.0.202011040924\tools\arm-none-eabi\bin\ld.exe: ./out/startup_stm32g431xx.o:(.text+0xc): undefined reference to `_sbss'
c:\st\stm32cubeide_1.6.0\stm32cubeide\plugins\com.st.stm32cube.ide.mcu.externaltools.gnu-tools-for-stm32.9-2020-q2-update.win32_1.5.0.202011040924\tools\arm-none-eabi\bin\ld.exe: ./out/startup_stm32g431xx.o:(.text+0x10): undefined reference to `_ebss'
c:\st\stm32cubeide_1.6.0\stm32cubeide\plugins\com.st.stm32cube.ide.mcu.externaltools.gnu-tools-for-stm32.9-2020-q2-update.win32_1.5.0.202011040924\tools\arm-none-eabi\bin\ld.exe: ./out/startup_stm32g431xx.o: in function `LoopForever':
B:/STM32/G4/Examples/mc_comm_lib GNU mk9p0/../../Nimbus/PAL/SRC/startup_stm32g431xx.asm:63: undefined reference to `_estack'
c:\st\stm32cubeide_1.6.0\stm32cubeide\plugins\com.st.stm32cube.ide.mcu.externaltools.gnu-tools-for-stm32.9-2020-q2-update.win32_1.5.0.202011040924\tools\arm-none-eabi\bin\ld.exe: B:/STM32/G4/Examples/mc_comm_lib GNU mk9p0/../../Nimbus/PAL/SRC/startup_stm32g431xx.asm:67: undefined reference to `_sdata'
c:\st\stm32cubeide_1.6.0\stm32cubeide\plugins\com.st.stm32cube.ide.mcu.externaltools.gnu-tools-for-stm32.9-2020-q2-update.win32_1.5.0.202011040924\tools\arm-none-eabi\bin\ld.exe: B:/STM32/G4/Examples/mc_comm_lib GNU mk9p0/../../Nimbus/PAL/SRC/startup_stm32g431xx.asm:69: undefined reference to `_sidata'
c:\st\stm32cubeide_1.6.0\stm32cubeide\plugins\com.st.stm32cube.ide.mcu.externaltools.gnu-tools-for-stm32.9-2020-q2-update.win32_1.5.0.202011040924\tools\arm-none-eabi\bin\ld.exe: B:/STM32/G4/Examples/mc_comm_lib GNU mk9p0/../../Nimbus/PAL/SRC/startup_stm32g431xx.asm:87: undefined reference to `_siccmram'
c:\st\stm32cubeide_1.6.0\stm32cubeide\plugins\com.st.stm32cube.ide.mcu.externaltools.gnu-tools-for-stm32.9-2020-q2-update.win32_1.5.0.202011040924\tools\arm-none-eabi\bin\ld.exe: B:/STM32/G4/Examples/mc_comm_lib GNU mk9p0/../../Nimbus/PAL/SRC/startup_stm32g431xx.asm:93: undefined reference to `_sccmram'
c:\st\stm32cubeide_1.6.0\stm32cubeide\plugins\com.st.stm32cube.ide.mcu.externaltools.gnu-tools-for-stm32.9-2020-q2-update.win32_1.5.0.202011040924\tools\arm-none-eabi\bin\ld.exe: B:/STM32/G4/Examples/mc_comm_lib GNU mk9p0/../../Nimbus/PAL/SRC/startup_stm32g431xx.asm:94: undefined reference to `_eccmram'
c:\st\stm32cubeide_1.6.0\stm32cubeide\plugins\com.st.stm32cube.ide.mcu.externaltools.gnu-tools-for-stm32.9-2020-q2-update.win32_1.5.0.202011040924\tools\arm-none-eabi\bin\ld.exe: B:/STM32/G4/Examples/mc_comm_lib GNU mk9p0/../../Nimbus/PAL/SRC/startup_stm32g431xx.asm:100: undefined reference to `_sbss'
c:\st\stm32cubeide_1.6.0\stm32cubeide\plugins\com.st.stm32cube.ide.mcu.externaltools.gnu-tools-for-stm32.9-2020-q2-update.win32_1.5.0.202011040924\tools\arm-none-eabi\bin\ld.exe: B:/STM32/G4/Examples/mc_comm_lib GNU mk9p0/../../Nimbus/PAL/SRC/startup_stm32g431xx.asm:101: undefined reference to `_ebss'
c:\st\stm32cubeide_1.6.0\stm32cubeide\plugins\com.st.stm32cube.ide.mcu.externaltools.gnu-tools-for-stm32.9-2020-q2-update.win32_1.5.0.202011040924\tools\arm-none-eabi\bin\ld.exe: ./out/startup_stm32g431xx.o:(.isr_vector+0x0): undefined reference to `_estack'
collect2.exe: error: ld returned 1 exit status

Do you know what is my problem? How can I resolve it? 

Thanks.