When building for iOS 6 as target (--host=arm-apple-darwin) with load disabled (--disable-load), two problems occur:
* The declaration of TclpLoadMemory differs from its definition.
* Some defines do not distinguish between __APPLE__ and ios/macosx.

diff -rupN tcl8.6.1.orig/generic/tclLoadNone.c tcl8.6.1/generic/tclLoadNone.c
--- tcl8.6.1.orig/generic/tclLoadNone.c	2013-09-19 21:04:14.000000000 +0200
+++ tcl8.6.1/generic/tclLoadNone.c	2014-07-29 08:57:30.000000000 +0200
@@ -104,7 +104,7 @@ TclpLoadMemory(
     int size,			/* Dummy: unused by this implementation */
     int codeSize,		/* Dummy: unused by this implementation */
     Tcl_LoadHandle *loadHandle,	/* Dummy: unused by this implementation */
-    Tcl_FSUnloadFileProc **unloadProcPtr)
+    Tcl_FSUnloadFileProc **unloadProcPtr, int flags)
 				/* Dummy: unused by this implementation */
 {
     Tcl_SetObjResult(interp, Tcl_NewStringObj("dynamic loading from memory "
diff -rupN tcl8.6.1.orig/unix/tclUnixPort.h tcl8.6.1/unix/tclUnixPort.h
--- tcl8.6.1.orig/unix/tclUnixPort.h	2013-09-19 21:04:17.000000000 +0200
+++ tcl8.6.1/unix/tclUnixPort.h	2014-07-29 11:01:56.000000000 +0200
@@ -541,7 +541,11 @@ extern int errno;
  *---------------------------------------------------------------------------
  */
 
-#if defined(__APPLE__) && defined(__DYNAMIC__)
+#ifdef __APPLE__
+#include "TargetConditionals.h"
+#endif
+
+#if defined(__APPLE__) && defined(__DYNAMIC__) && TARGET_OS_MAC
 #   include <crt_externs.h>
 #   define environ	(*_NSGetEnviron())
 #   define USE_PUTENV	1

It looks like your configuration is trying to link against the wrong architecture (i386) instead of arm.
Maybe there are some files remaining from a previous build? (make distclean)
Or the 'configure' was not set to cross-compile, e.g. --host=arm-apple-darwin

As far as testing is concerned, the ARM build of Tcl for iOS works only on a jailbroken device out of the box.
However It may be possible to build the Tcl library as framework for iOS (--enable-framework) and use it in a sample iOS application. This application will then have to be signed and deployed on a registered developer device, which requires an Apple developer account (charges apply - approx $100/y).

I've opened an ios branch for these patches, but I'm not sure I'm doing the build right. I get these errors when running make per your instructions: 

ld: warning: ignoring file tclAppInit.o, file was built for unsupported file format ( 0xCF 0xFA 0xED 0xFE 0x07 0x00 0x00 0x01 0x03 0x00 0x00 0x00 0x01 0x00 0x00 0x00 ) which is not the architecture being linked (i386): tclAppInit.o
ld: warning: ignoring file /Users/kevin/tcl-ios/unix/libtcl8.6.a, file was built for archive which is not the architecture being linked (i386): /Users/kevin/tcl-ios/unix/libtcl8.6.a
ld: warning: ignoring file libtclstub8.6.a, file was built for archive which is not the architecture being linked (i386): libtclstub8.6.a
Undefined symbols for architecture i386:
  "_main", referenced from:
     implicit entry/start for main executable
ld: symbol(s) not found for architecture i386

Also, I'm not sure how to test the build once I get something build--I refuse to jailbreak my iPhone. Do you know of a way to run this in the simulator, assuming I can get it to build?

Just glancing from the side, it appears that bitrot has
caused --disable-load to stop working.  At a minimum that
requires a fix, and is important not only on Apple systems.

It's an exciting opportunity to add a new platform too.
We appreciate the patience and assistance working through
the startup pains

compile with (Makefile syntax) in <tcldir>/unix/:
GCC_BIN=$(shell xcrun --sdk iphoneos --find gcc)
IOS_SDK=$(shell xcrun --sdk iphoneos --show-sdk-path)
CFLAGS=-arch armv7 -Os -F$(IOS_SDK)/System/Library/Frameworks -isysroot "$(IOS_SDK)" -Wimplicit -pipe -miphoneos-version-min=6.1 -no-cpp-precomp -I$(IOS_SDK)/usr/include/

all:
    ./configure CC="$(GCC_BIN)" CFLAGS="$(CFLAGS)" --host=arm-apple-darwin --disable-load
    make
    make install DESTDIR=/tmp/tcl-root

Note: The unsigned software runs on a jailbroken iOS device, e.g. iPod touch 4g, iPhone 4, ...

Also, the first of the proposed changes may allow --disable-load for other platforms as well. This is not iOS or Apple specific. The second of the proposed changes (#ifdef...) does no harm whatsoever, as long as Tcl still compiles on OSX.

iOS is not a supported platform and I am not familiar with steps required to compile for it, or test builds. Please provide more information on the steps you are following to achieve these ends.

Assigned to our Apple person.