/usr/include doesn't exist in Catalina

[Susumu Yamazaki]

Describe the bug
Pelemay can't mix compile in case of CC=gcc because /usr/include doesn't exist in Catalina.

To Reproduce
Steps to reproduce the behavior:

1. Use Pelemay in some source code
2. set export CC=gcc
3. Run in the command 'mix compile'
4. See error:

.../erl_drv_nif.h:158:12: fatal error: sys/types.h: No such file or directory
  158 | #  include <sys/types.h>
      |            ^~~~~~~~~~~~~
compilation terminated.

Expected behavior

Makefile should be added the following in case of macOS:

  `CFLAGS += -I`xcrun --show-sdk-path`/usr/include

Screenshots
None.

Desktop (please complete the following information):

In case of Catalina

Additional context
None.

[Andy Chang]

Hi, sorry to interrupt, I encountered this error: "ld: library not found for -lSystem" on macOS 10.15.5 and have no idea to fix it.