ldlinux: Avoid initialised data memory corruption

ldlinux: Avoid initialised data memory corruption

We can't realloc() 'PATH' because realloc() may just extend the
malloc'd region if the adjacent region is free, as opposed to
allocating a new region and then copying the data. This behaviour is
fine in most circumstances but not with initialised string data, such
as 'PATH'. The reason is that other string data pointers may point to
characters in 'PATH' and if we modify it after realloc()'ing, we'll
appear to corrupt unrelated string data.

For example, the string "/" is used in chdir() and the address of that
string is the last "/" in 'PATH'. If we realloc() and then append
"foo" to 'PATH' the string pointer in chdir() will now point to "/foo".

Initialise 'PATH' at runtime using malloc() and free() to avoid
corrupting string data.

Signed-off-by: Matt Fleming <matt.fleming@intel.com>