I picked up Tcl is compiles with this default parameter --enable-shared=on. For that reason I didn't have a libtcl8.6.a file in my lib directory. When I used libtcl8.6.so it failed to compile wapptclsh and I know it was for obvious reasons.

I recompiled Tcl8.6 as follows;
$ ./configure --prefix=/export/apps/tcl868 --enable-shared=off --enable-64bit
$ make && make install

Then tried to compile wapptclsh as follows; 

xxx@hostname:/export/apps/wapp$ cat Makefile
#!/usr/bin/make

CC = gcc -Os -static
OPTS = -DSQLITE_ENABLE_DESERIALIZE
TCLLIB = /export/apps/tcl861/lib/libtcl8.6.a -lm -lz -lpthread -ldl
TCLINC = /export/apps/tcl861/include
TCLSH = tclsh

all: wapptclsh

wapptclsh: wapptclsh.c
	$(CC) -I. -I$(TCLINC) -o $@ $(OPTS) wapptclsh.c $(TCLLIB)

wapptclsh.c:	wapptclsh.c.in wapp.tcl wapptclsh.tcl tclsqlite3.c mkccode.tcl
	$(TCLSH) mkccode.tcl wapptclsh.c.in >$@

clean:	
	rm wapptclsh wapptclsh.c


xxx@ohstname:/export/apps/wapp$ make
gcc -Os -static -I. -I/export/apps/tcl861/include -o wapptclsh -DSQLITE_ENABLE_DESERIALIZE wapptclsh.c /export/apps/tcl861/lib/libtcl8.6.a -lm -lz -lpthread -ldl
/export/apps/tcl861/lib/libtcl8.6.a(tclLoadDl.o): In function `TclpDlopen':
tclLoadDl.c:(.text+0x1de): warning: Using 'dlopen' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking
/export/apps/tcl861/lib/libtcl8.6.a(tclUnixCompat.o): In function `TclpGetGrGid':
tclUnixCompat.c:(.text+0x41c): warning: Using 'getgrgid_r' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking
/export/apps/tcl861/lib/libtcl8.6.a(tclUnixCompat.o): In function `TclpGetGrNam':
tclUnixCompat.c:(.text+0x31c): warning: Using 'getgrnam_r' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking
/export/apps/tcl861/lib/libtcl8.6.a(tclUnixCompat.o): In function `TclpGetPwNam':
tclUnixCompat.c:(.text+0x114): warning: Using 'getpwnam_r' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking
/export/apps/tcl861/lib/libtcl8.6.a(tclUnixCompat.o): In function `TclpGetPwUid':
tclUnixCompat.c:(.text+0x214): warning: Using 'getpwuid_r' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking
/export/apps/tcl861/lib/libtcl8.6.a(tclIOSock.o): In function `TclCreateSocketAddress':
tclIOSock.c:(.text+0x2c9): warning: Using 'getaddrinfo' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking
/export/apps/tcl861/lib/libtcl8.6.a(tclUnixCompat.o): In function `TclpGetHostByAddr':
tclUnixCompat.c:(.text+0x593): warning: Using 'gethostbyaddr_r' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking
/export/apps/tcl861/lib/libtcl8.6.a(tclUnixCompat.o): In function `TclpGetHostByName':
tclUnixCompat.c:(.text+0x4f4): warning: Using 'gethostbyname_r' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking
/export/apps/tcl861/lib/libtcl8.6.a(tclIOSock.o): In function `TclSockGetPort':
tclIOSock.c:(.text+0x55): warning: Using 'getservbyname' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking

xxx@hostname:/export/apps/wapp$ ls -la
total 31252
drwxr-xr-x  7 bwaan bwaan    4096 Sep 28 17:37 .
drwxr-xr-x 21 bwaan bwaan    4096 Sep 24 07:52 ..
drwxr-xr-x  2 bwaan bwaan    4096 Sep 22 19:26 docs
-rw-r--r--  1 bwaan bwaan     611 Sep 22 19:26 encode-binary-file.tcl
drwxr-xr-x  2 bwaan bwaan    4096 Sep 22 19:26 examples
-rw-r--r--  1 bwaan bwaan     444 Sep 28 17:31 Makefile
-rw-r--r--  1 bwaan bwaan     431 Sep 22 19:26 Makefile.macos
-rw-r--r--  1 bwaan bwaan     432 Sep 23 06:08 Makefile.orig
-rwxr-xr-x  1 bwaan bwaan    3002 Sep 22 19:26 mkccode.tcl
drwxrwxr-x  2 bwaan bwaan    4096 Sep 23 05:56 proj
-rw-r--r--  1 bwaan bwaan    1528 Sep 22 19:26 README.md
-rw-r--r--  1 bwaan bwaan 8264893 Sep 22 19:26 tclsqlite3.c
drwxr-xr-x  2 bwaan bwaan    4096 Sep 22 19:26 tests
-rw-r--r--  1 bwaan bwaan   31464 Sep 22 19:26 wapp.tcl
-rwxrwxr-x  1 bwaan bwaan 5009208 Sep 28 17:35 wapptclsh
-rw-rw-r--  1 bwaan bwaan 8303748 Sep 24 08:11 wapptclsh.c
-rw-r--r--  1 bwaan bwaan    1670 Sep 22 19:26 wapptclsh.c.in
-rw-r--r--  1 bwaan bwaan     361 Sep 22 19:26 wapptclsh.tcl

It works but my compilation had errors, not sure what i could have missed.