CMake: Skip empty link.txt lines (#13845)

In the implementation of "cmake -E cmake_link_script", skip lines from
the input file that are empty or contain only whitespace.  Do not try to
run a child with no command line.
KWSys 2013-01-10 (608d6b47)

Extract upstream KWSys using the following shell commands.

$ git archive --prefix=upstream-kwsys/ 608d6b47 | tar x
$ git shortlog --no-merges --abbrev=8 --format='%h %s' fc60c8b8..608d6b47
Rolf Eike Beer (6):
      297758a5 SystemInformation: fix conversion warning
      79ef34ef SystemInformation: fix calling kwsysProcess_WaitForData()
      f1068caf SystemInformation: speed up copying process data
      7dfc27d5 SystemInformation: check CPU vendor and SSE support on OpenBSD
      494d9d7a SystemInformation: get stepping code on Intel Macs
      608d6b47 SystemInformation: determine processor features on Intel Macs

Change-Id: I7f5bc5b7af2bf7d4e5c1ee291c286add0f17a7d5
Merge branch 'upstream-kwsys' into update-kwsys
Don't include generator expressions in old-style link handling.

Don't add generator expressions to variables which are used
for CMP0003, CMP0004, and the old-style _LIB_DEPENDS content. They
will not be evaluated when read anyway and would probably confuse
the code reading them.

This makes it legitimate to use target_link_libraries with generator
expressions as arguments.
Document the use of generator expressions in new commands.
Add the TARGET_DEFINED generator expression

This tests whether the parameter is a usable target.
KWSys 2013-01-14 (6fa1c99f)

Extract upstream KWSys using the following shell commands.

$ git archive --prefix=upstream-kwsys/ 6fa1c99f | tar x
$ git shortlog --no-merges --abbrev=8 --format='%h %s' 608d6b47..6fa1c99f
Brad King (1):
      84827cc1 Process: Avoid argv[0]==NULL from parsing empty command line

Rolf Eike Beer (8):
      e041cd66 SystemInformation: factor out QueryMemoryBySysconf()
      ea850fa0 SystemInformation: factor out QueryProcessorBySysconf()
      57f06d49 SystemInformation: count processors with sysconf() on Solaris
      c6057a06 SystemInformation: fix "Multi-character character constant"
      5a27bd4f SystemInformation: make IsHyperThreadingSupported() return bool
      342c0ad2 SystemInformation: query memory size with sysconf() on Solaris
      f0b857c1 SystemInformation: cache result of IsHyperThreadingSupported()
      ab0c2a09 SystemInformation: try using assembler with BorlandC

Change-Id: I072371ed35eed892a5ef62a9e9e6cad734e961d9
Merge branch 'upstream-kwsys' into update-kwsys
CMake Nightly Date Stamp
Add a way to check INTERFACE user property compatibility.
Merge topic 'fix-empty-link-line-crash'

8ff1d47 CMake: Skip empty link.txt lines (#13845)
Merge topic 'compatible-INTERFACE-user-properties'

7171fd0 Add a way to check INTERFACE user property compatibility.
Merge topic 'tll-allow-genex'

1da7502 Don't include generator expressions in old-style link handling.
Merge topic 'commands-genex-docs'

7c7b94f Document the use of generator expressions in new commands.
Merge topic 'TARGET_DEFINED-genex'

2bee6f5 Add the TARGET_DEFINED generator expression
Merge topic 'update-kwsys'

e2c756f Merge branch 'upstream-kwsys' into update-kwsys
4ba0ac7 KWSys 2013-01-14 (6fa1c99f)
6f57a90 Merge branch 'upstream-kwsys' into update-kwsys
6318834 KWSys 2013-01-10 (608d6b47)
Strip consecutive semicolons when preprocessing genex strings.
Don't write a comment in the export file without the code.
Only generate one check per missing target.
Move the exported check for dependencies of targets

Check only once, in the Config.cmake file, instead of once in each
Config-<cfg>.cmake file.