Apple's linker performs by-content merges of string constants in the
magical "cstring" section.  We do not want this to happen to
_master_location since we modify it later, which would also modify any
merged strings.

The "cstring" section is only supposed to contain values following C
string syntax, i.e. any number of non-NUL bytes followed by a single
NUL byte.  So actually _master_location should already be disqualified
from placement in this section since it has MAXPATHLEN NUL bytes at
the end instead of just one.  However, in the case of const char[]
variables initialized from a string literal there is a bug/misfeature
in gcc that it only considers the literal, not the initialized
variable as a whole.  Thus, we need to add at least one of the extra
NUL bytes to the string literal for gcc to do the right thing.  This
does not change the actual variable value in any way.