Fix OS X crossbuilds for arm

 - Fixed missing variable interpolation because of single quotes
 - Replaced /bin/sh in gen_uEnv.txt.sh with /usr/bin/env bash as the default
   echo doesn't support '-n'
 - Fixed some whitespace errors
 - A succesful build requires for now to skip the gold linker on OSX.

Change-Id: Id09bf52f45252026e3a58b74e8448ea24a0dab12
Fix build error on OSX

When building Gold on OSX 10.9 and Clang 6.0, the build process fails
with the error:

In file included from /Users/thomas/minix/tools/binutils/../../external/gpl3/binutils/dist/gold/binary.cc:31:
In file included from /Users/thomas/minix/tools/binutils/../../external/gpl3/binutils/dist/gold/stringpool.h:23:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/string:438:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/cwchar:107:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/cwctype:54:
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/cctype:51:72: error: use of undeclared identifier 'do_not_use_isalnum_with_safe_ctype'
inline _LIBCPP_INLINE_VISIBILITY int __libcpp_isalnum(int __c) {return isalnum(__c);}

Signed-off-by: Thomas Veerman <tveerman@gmail.com>
Change-Id: Ib7ca13a51e83c31bb3020d755e04b308aeacde5d