m4: fix musl checks.
m4: fix musl checks.

Closes #9358.

coredumb/void-packages,floGik/void-packages,floGik/void-packages,kulinacs/void-packages,coredumb/void-packages,coredumb/void-packages,floGik/void-packages,juliendehos/void-packages,kulinacs/void-packages,coredumb/void-packages,juliendehos/void-packages,juliendehos/void-packages,NeoChontrix/void-packages,EaterOfCode/void-packages,kulinacs/void-packages,necrophcodr/void-packages,NeoChontrix/void-packages,EaterOfCode/void-packages,coredumb/void-packages,floGik/void-packages,kulinacs/void-packages,EaterOfCode/void-packages,juliendehos/void-packages,floGik/void-packages,floGik/void-packages,juliendehos/void-packages,necrophcodr/void-packages,EaterOfCode/void-packages,NeoChontrix/void-packages,necrophcodr/void-packages,NeoChontrix/void-packages,necrophcodr/void-packages,kulinacs/void-packages,juliendehos/void-packages,EaterOfCode/void-packages,kulinacs/void-packages,NeoChontrix/void-packages,coredumb/void-packages,NeoChontrix/void-packages,necrophcodr/void-packages