Thanks! Is it the make program itself which tries to run /bin/sh, or does it try to run a file from a project which has a #!/bin/sh start?

If it's GNU make itself which tries to call /bin/sh directly, that could be patched from my side. But if it is a script from a file, you have to make the shebang replacement #!/bin/sh -> #!${PREFIX}/bin/sh yourself on all script files to be executed - there is a simple termux-fix-shebang script installed by default for that!