[Automake] Scripts for generated build targets do not necessarily produce their output

[Automake] Scripts for generated build targets do not necessarily produce their output
https://bugs.webkit.org/show_bug.cgi?id=126378

Reviewed by Carlos Garcia Campos.

Source/JavaScriptCore:

* GNUmakefile.am: Touch the build targets that are generated through helper scripts that don't
assure the output is generated every time the script is invoked, most commonly due to unchanged
input. This assures the build targets are up-to-date and can't be older that their dependencies,
which would result in constant regeneration at every build.

Source/WebCore:

* GNUmakefile.am: Touch the build targets that are generated through helper scripts that don't
assure the output is generated every time the script is invoked, most commonly due to unchanged
* bindings/gobject/GNUmakefile.am: Simply move the gdom-gen-symbols file into the output file
instead of copying it if the contents differ and removing it. This again ensures that the output
file is always newer than its dependencies, even if the input hasn't changed.

Source/WebKit2:

* GNUmakefile.am: Don't pass the -n option to the ln command that links the build's include
directories to actual source directories. This doesn't replace the original symbolic link,
which can lead to the actual link being older than its dependencies and subsequent constant
relinking at every build.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@161497 268f45cc-cd09-0410-ab3c-d52691b4dbfc