Xcode: Fix compiler id detection for iOS tools (#15214)

Since commit 0cce556b (Xcode: Use sysroot and deployment target to
identify compiler, 2014-04-29) our compiler id detection project uses
the target platform SDK in case Xcode selects a different compiler based
on it.  Now the compiler id project actually compiles with the target
compiler and SDK when cross-compiling.

The iOS tools do not support the 'com.apple.product-type.tool' product
type we use in our compiler id detection project.  When targeting
iPhone, use product type 'com.apple.product-type.bundle.unit-test'
instead.
Xcode: Fix compiler id detection when code signing is required

The iOS product type 'com.apple.package-type.bundle.unit-test' requires
code signing on Xcode 6.  Other iOS target types do too.  Until CMake
learns to add the CODE_SIGN_IDENTITY build attribute itself, toolchain
files can set CMAKE_XCODE_ATTRIBUTE_CODE_SIGN_IDENTITY to tell the Xcode
generator to add the attribute.  Teach CMakeDetermineCompilerId to
recognize this variable and add the CODE_SIGN_IDENTITY build attribute
to the compiler id project.
Modules: Format documentation to avoid over-long preformatted lines

Convert several preformatted code block literals that enumerate lists of
options or variables to use reST definition lists instead.  Manually
wrap other long lines in code blocks.
Help: Wrap long ctest_submit signature line
Help: Clarify formatting of CPACK_WIX_ACL documentation
Help/manual: Avoid long lines in code blocks

Update the wording of some examples to avoid long lines in code blocks.
Otherwise the formatted documentation can exceed certain column width
limitations.
Merge branch 'doc-line-lengths' into release
Merge branch 'xcode-ios-compiler-id' into release