component/ghostscript: Workaround for slaprunner paths with double slashs

This tessdata path will be included in cpp code by pre-processor macros
https://github.com/ArtifexSoftware/ghostpdl/blob/gs9.54.0/base/tessocr.cpp#L188-L193
Since // is the marker for a comment in cpp and as documented in
https://gcc.gnu.org/onlinedocs/cpp/Stringizing.html "Comments are replaced by
whitespace long before stringizing happens, so they never appear in stringized
text", the STRINGIFY/STRINGIFY2 approach of including a path does not work
when the path contain // , because anything after // is considered a comment
and is not included, causing errors like this when using ghostscript with OCR
in webrunner:

    $ strace -e open -o open.strace /srv/slapgrid/slappart42/srv/runner/shared/ghostscript/4387fe7a8d2034ac5691d43b58134248/bin/gs -sDEVICE=ocr
    GPL Ghostscript 9.54.0 (2021-03-30)
    Copyright (C) 2021 Artifex Software, Inc.  All rights reserved.
    This software is supplied under the GNU AGPLv3 and comes with NO WARRANTY:
    see the file COPYING for details.
    Error opening data file ./eng.traineddata
    Please make sure the TESSDATA_PREFIX environment variable is set to your "tessdata" directory.
    Failed loading language 'eng'
    Tesseract couldn't load any languages!
    **** Unable to open the initial device, quitting.
    $ grep eng open.strace
    open("./eng.traineddata", O_RDONLY)     = -1 ENOENT (No such file or directory)
    open("/srv/slapgrid/slappart42/srv/eng.traineddata", O_RDONLY) = -1 ENOENT (No such file or directory)
    open("eng.traineddata", O_RDONLY)       = -1 ENOENT (No such file or directory)

eng.traineddata is looked up in /srv/slapgrid/slappart42/srv/ because
ghostscript was configured with:

   --with-tessdata=/srv/slapgrid/slappart42/srv//runner//shared/ghostscript/4387fe7a8d2034ac5691d43b58134248/share/tessdata/

and everything after // was stripped.

This was reported upstream as https://bugs.ghostscript.com/show_bug.cgi?id=703905

More about the case of // in slaprunner paths was on commit eb544196
(slparunner: document the reasons why we keep srv//slaprunner, 2019-10-10)