What generates pg_config.h?

Hi,

I have postgres 9.5 and 9.6 installed. pg_config points to 9.6.
I am trying to compile a postgresql plugin (Timescaledb). I am getting an
error:
-----------------------------------------------
/usr/include/postgresql/pg_config.h:733:0: warning: "PACKAGE_VERSION"
redefined
#define PACKAGE_VERSION "10.0"
^
In file included from /usr/include/postgresql/9.6/server/c.h:53:0,
from /usr/include/postgresql/9.6/server/postgres.h:47,
from /mnt/data/timescaledb/src/init.c:1:
/usr/include/postgresql/9.6/server/pg_config.h:740:0: note: this is the
location of the previous definition
#define PACKAGE_VERSION "9.6.5"
-----------------------------------------------------

The command pg_config gives the following:

---------------------------------------
BINDIR = /usr/lib/postgresql/9.6/bin
DOCDIR = /usr/share/doc/postgresql-doc-9.6
HTMLDIR = /usr/share/doc/postgresql-doc-9.6
INCLUDEDIR = /usr/include/postgresql
PKGINCLUDEDIR = /usr/include/postgresql
INCLUDEDIR-SERVER = /usr/include/postgresql/9.6/server
LIBDIR = /usr/lib/x86_64-linux-gnu
PKGLIBDIR = /usr/lib/postgresql/9.6/lib
LOCALEDIR = /usr/share/locale
MANDIR = /usr/share/postgresql/9.6/man
SHAREDIR = /usr/share/postgresql/9.6
SYSCONFDIR = /etc/postgresql-common
PGXS = /usr/lib/postgresql/9.6/lib/pgxs/src/makefiles/pgxs.mk
CONFIGURE = '--with-tcl' '--with-perl' '--with-python' '--with-pam'
'--with-openssl' '--with-libxml' '--with-libxslt'
'--with-tclconfig=/usr/lib/x86_64-linux-gnu/tcl8.6'
'--with-includes=/usr/include/tcl8.6' 'PYTHON=/usr/bin/python'
'--mandir=/usr/share/postgresql/9.6/man'
'--docdir=/usr/share/doc/postgresql-doc-9.6'
'--sysconfdir=/etc/postgresql-common' '--datarootdir=/usr/share/'
'--datadir=/usr/share/postgresql/9.6'
'--bindir=/usr/lib/postgresql/9.6/bin'
'--libdir=/usr/lib/x86_64-linux-gnu/' '--libexecdir=/usr/lib/postgresql/'
'--includedir=/usr/include/postgresql/' '--enable-nls'
'--enable-integer-datetimes' '--enable-thread-safety' '--enable-tap-tests'
'--enable-debug' '--disable-rpath' '--with-uuid=e2fs' '--with-gnu-ld'
'--with-pgport=5432' '--with-system-tzdata=/usr/share/zoneinfo'
'--with-systemd' 'CFLAGS=-g -O2 -fstack-protector-strong -Wformat
-Werror=format-security -fPIC -pie -fno-omit-frame-pointer'
'LDFLAGS=-Wl,-Bsymbolic-functions -Wl,-z,relro -Wl,-z,now' '--with-gssapi'
'--with-ldap' '--with-includes=/usr/include/mit-krb5'
'--with-libs=/usr/lib/mit-krb5'
'--with-libs=/usr/lib/x86_64-linux-gnu/mit-krb5' '--with-selinux'
'CPPFLAGS=-Wdate-time -D_FORTIFY_SOURCE=2'
CC = gcc
CPPFLAGS = -DFRONTEND -Wdate-time -D_FORTIFY_SOURCE=2 -D_GNU_SOURCE
-I/usr/include/libxml2 -I/usr/include/mit-krb5
CFLAGS = -Wall -Wmissing-prototypes -Wpointer-arith
-Wdeclaration-after-statement -Wendif-labels -Wmissing-format-attribute
-Wformat-security -fno-strict-aliasing -fwrapv -fexcess-precision=standard
-g -g -O2 -fstack-protector-strong -Wformat -Werror=format-security -fPIC
-pie -fno-omit-frame-pointer
CFLAGS_SL = -fPIC
LDFLAGS = -L../../src/common -Wl,-Bsymbolic-functions -Wl,-z,relro
-Wl,-z,now -L/usr/lib/x86_64-linux-gnu/mit-krb5 -Wl,--as-needed
LDFLAGS_EX =
LDFLAGS_SL =
LIBS = -lpgcommon -lpgport -lselinux -lxslt -lxml2 -lpam -lssl -lcrypto
-lgssapi_krb5 -lz -ledit -lrt -lcrypt -ldl -lm
VERSION = PostgreSQL 9.6.5
-------------------------------------------------

So my question is: what is generating the
/usr/include/postgresql/pg_config.h file? Why is it different than the
/usr/include/postgresql/9.6/server/pg_config.h file?

Thanks!

Travis