stdio.h Not Found – Fixing ‘stdio.h’ File Not Found Error in GCC

When I compile a package, I got the following error:

$ make
clang -Wall -Wmissing-prototypes -Wpointer-arith -Wdeclaration-after-statement -Wendif-labels -Wmissing-format-attribute -Wformat-security -fno-strict-aliasing -fwrapv -Wno-unused-command-line-argument -O2  -I/usr/local/include/scws  -I. -I./ -I/usr/local/Cellar/postgresql/11.3/include/server -I/usr/local/Cellar/postgresql/11.3/include/internal -I/usr/local/Cellar/icu4c/64.2/include -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.14.sdk -I/usr/local/opt/openssl/include -I/usr/local/opt/readline/include -I/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.14.sdk/usr/include/libxml2   -c -o zhparser.o zhparser.c
clang: warning: no such sysroot directory: '/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.14.sdk' [-Wmissing-sysroot]
In file included from zhparser.c:10:
In file included from /usr/local/Cellar/postgresql/11.3/include/server/postgres.h:46:
/usr/local/Cellar/postgresql/11.3/include/server/c.h:59:10: fatal error: 'stdio.h' file not found
#include <stdio.h>
         ^~~~~~~~~
1 error generated.

When I search this error online, all the online problems are not having header files at /usr/include/. But when I check the directory, it has many header files

$ ls -l /usr/include/stdio.h
-r--r--r--  1 root  wheel  16319 Jan 22  2018 /usr/include/stdio.h

$ ls -l /usr/include/ | wc -l
     266

So, what can I do in my case?

Thanks a lot.

Edited: I updated the error output. I just found out it had a warning too: clang: warning: no such sysroot directory: '/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.14.sdk', But I have MacOSX10.13.sdk instead because I am running MacOSX10.13. I have no ideas why it's looking for 10.14 sdk and not sure if this is the root cause or not.