cmMakefile: make some methods take const std::string& instead of const char*

Most callers already have a std::string, on which they called c_str() to pass it
into these methods, which internally converted it back to std::string. Pass a
std::string directly to these methods now, avoiding all these conversions.
Those methods that only pass in a const char* will get the conversion to
std::string now only once.
Help: Document CMAKE_OSX_* variables

Add documentation entries for variables

 CMAKE_OSX_ARCHITECTURES
 CMAKE_OSX_DEPLOYMENT_TARGET
 CMAKE_OSX_SYSROOT

Explain what each does and when/how they should be set.
Xcode: Remove dead code

Variable 'ext' already checked for equality to "xib" so remove the
branch that will never be executed.
Xcode: Fix storyboard view

Images and xib files must have 'lastKnownFileType' attribute to be
displayed correctly. If xib file has attribute 'explicitFileType' it is
displayed as raw xml. If static image has attribute 'explicitFileType'
it is displayed as question mark on storyboard.
Improve ld flags for CMake itself on Linux/HPPA

Workaround binutils bug by only marking unique section starting by
".text._".

This adds the HPPA workaround improved in commit b22a0f15 (bootstrap:
improve ld flag for Linux/HPPA builds, 2014-01-14) not only to the
bootstrap, but also to the normal build.
Merge topic 'cmmakefile-const'

c768e398 cmMakefile: make some methods take const std::string& instead of const char*
Merge topic 'doc-osx-vars'

45056264 Help: Document CMAKE_OSX_* variables
Merge topic 'xcode-storyboard-view'

1ce02ebf Xcode: Fix storyboard view
d9f1f917 Xcode: Remove dead code
Merge topic 'hppa-binutils-flag'

8f2c2ccb Improve ld flags for CMake itself on Linux/HPPA