Creation of svg images for formulas with inkscape

Based on the implementation as mentioned in #7578 to add the possibilities to generated svg images for formulas

- When running with inkscape 92.3 / 92.4 on Cygwin /Windows there were no images generated as the `-o` flag didn't exist, the output file had to be specified as part of the `-l`  (or `--export-plain-svg`) option
- For more flexibility the system is checked on existence of the `pdf2svg` and `inkscape` executables, so no compilations flags are necessary

1 files changed, 1 insertions, 0 deletions

diff --git a/src/portable.h b/src/portable.h
index 956ae41..6c215a8 100644
--- a/src/portable.h
+++ b/src/portable.h
@@ -44,6 +44,7 @@ namespace Portable
   void           setShortDir(void);
   const char *   strnstr(const char *haystack, const char *needle, size_t haystack_len);
   const char *   devNull();
+  const bool     checkForExecutable(const char *fileName);
 }