BUG: Regenerate HeaderTests' after .hxx files are removed.

The HeaderTests were not regenerated appropriately when only .hxx files
were moved around because the .hxx files were not included in the MD5 hash used
to keep track of module header contents.

Suggested-by: Bill Hoffman <bill.hoffman@kitware.com>

Change-Id: I1593cbedd1d221e191ee9c7d1df7085d6b5b78c7
STYLE: ITK_EXPORT had no use

The defintion of ITK_EXPORT was empty in all cases

This has been identified since 2003 as not being necessary
for builds. see https://issues.itk.org/jira/browse/ITK-3110

On Windows builds that need exports, they must
be unique per library, and that is not controlled by CMake now.

The PrintSelfCheck.tcl was the only remenant need for
This patch, and that is no longer being used, so that
file as been removed.

The ITK_EXPORT define was set to nothing and had no
known remaining purpose.  It was removed to make the
over all code easier to understand.  There was,
understandably, a bit of confusion about the
need for this being pervasive in the code.

It is currently backwards compatible to have
this in code, but at some future point it will
be removed.

On request of Brad Lowekamp ITK_EXPORT was retained as a placeholder
in the IO modules. This will assist with making IO shared libraries.

Change-Id: I91573177a9bec05ccc44e5f875fe977a4e6cb1d6
Merge topic 'JIRA_ITK-3110'

b788601 STYLE: ITK_EXPORT had no use
Merge topic 'HeaderTest'

9b640a5 BUG: Regenerate HeaderTests' after .hxx files are removed.
BUG: Disable aligned attribute to fix Apple GCC 4.2.1 seg fault

Commit 2f96c578 fixed the configure test checking if aligned
attributes were supported by the compiler. Then commit e906441e
disabled the test for Gcc 4.1 to prevent a similar error.

This commit ensures that the configure test also excludes Apple
Gcc 4.2.1 (without llvm support) by forcing the configure test to
be in "Debug" mode.

When this issue was first encountered by Brad, the problem was occurring
in Debug mode and he narrowed it down to the block of code in the try_compile
and tried to use it as a detector. Slicer appears to have encountered the
same issue in release mode, but the bug detector only detects it in Debug
mode.

Fixes #3172 - See https://itk.icts.uiowa.edu/jira/browse/ITK-3172

Co-authored-by: Bradley Lowekamp <blowekamp@mail.nih.gov>

Change-Id: I67c870d8f68b0fd2fafaf470738bf125887165d7
Merge branch 'ITK-3172-unsupported-aligned-attribute-gcc421' into release

Change-Id: Ibf85f508674555692521f7efabb38b406f2cb56d
Merge branch 'release'

Change-Id: I2cc64dd62322682117872970fb191ada2105bf58