gen-def.py: pass headers as arguments so that msys2 can convert posix paths

let python's parse command-line args as usual

When one is not using the msys2 python, the header files that are passed in as environment
variable cannot be found.

https://ci.appveyor.com/project/fonttools/ttfautohint-py/build/1.0.65/job/rkremny4jjid9nl2#L803

This is because msys2 shell and make use POSIX paths (e.g. /c/Users/clupo/...)
whereas non-msys2 python.exe uses native Windows paths (e.g. C:\Users\clupo\...).

Msys2 will automatically convert command line arguments (but not environment variables) from
POSIX to Windows paths when calling a native win32 executable, so we pass the header paths
as arguments instead of environment variables.

This way the gen-def.py script can support both mingw python running in an MSYS2 shell, and
native win32 python.

Fixes #481

Completes #1037 and fixes #1035.

Disable vectorization for now.  To correctly use them, we should
use posix_memalign() to allocate them.  Otherwise, can cause
misaligned access.

https://bugs.chromium.org/p/chromium/issues/detail?id=860184

../../src/hb-ot-layout-gsubgpos-private.hh:391:18: warning: missed loop optimization, the loop counter may overflow [-Wunsafe-loop-optimizations]

From the new code (first paragraph is from the OT Devanagari spec.):

  /*   o Reorder matras:
   *
   *     If a pre-base matra character had been reordered before applying basic
   *     features, the glyph can be moved closer to the main consonant based on
   *     whether half-forms had been formed. Actual position for the matra is
   *     defined as “after last standalone halant glyph, after initial matra
   *     position and before the main consonant”. If ZWJ or ZWNJ follow this
   *     halant, position is moved after it.
   *
   * IMPLEMENTATION NOTES:
   *
   * It looks like the last sentence is wrong.  Testing, with Windows 7 Uniscribe
   * and Devanagari shows that the behavior is best described as:
   *
   * "If ZWJ follows this halant, matra is NOT repositioned after this halant.
   *  If ZWNJ follows this halant, position is moved after it."
   *
   * Test case, with Adobe Devanagari or Nirmala UI:
   *
   *   U+091F,U+094D,U+200C,U+092F,U+093F
   *   (Matra moves to the middle, after ZWNJ.)
   *
   *   U+091F,U+094D,U+200D,U+092F,U+093F
   *   (Matra does NOT move, stays to the left.)

Fixes https://github.com/harfbuzz/harfbuzz/issues/1070

Test case added with Adobe Devanagari.

The get_table imple was wrong, as table offsets in a dfont are
relative to the resource.  We were treating them as relative to
the big blob itself.  To be fixed.

Part of https://github.com/harfbuzz/harfbuzz/pull/1085

In collaboration with Behdad

From the issue:
"In this font, the virama,ya first forms a ligature, then decomposes back to
virama,ya. This causes those two to be marked parts of a MultipleSubst
sequence. When attaching the matra, we look for the first of the MultipleSubst
sequence because that's where we attach to (because of eg #740). In this case,
the first glyph in the MultipleSubst sequence is a mark, so we skip it and
attach to the base char before it."

Font in question is Nirmala UI from Windows 10. Test sequence:

  U+0926,U+094D,U+092F,U+0941

Fixes https://github.com/harfbuzz/harfbuzz/issues/1020

Fixes https://github.com/harfbuzz/harfbuzz/issues/1073

Indic shaper already had this check.  We removed it when forking
Khmer shaper by mistake.

Fixes https://bugzilla.mozilla.org/show_bug.cgi?id=1464623

Fixes #1081

Oops

* Handle EINTR on fallback reader
* Increase fallback reader limitation size limitation to 2 << 28
* Ensure _O_BINARY does exist if MMAP is used on Windows
  (maybe superfluous but makes me more confident)

Makes compiling without HAVE_ROUND on systems that do have it work.

Add one more "unlikely" annotation and use explicit nullptr check for more consistency.

And assign one bot to use the path always using NOMMAPFILEREADER token.

It's limited to 200mb so no more fun with using /dev/zero on hb-view!

In particular, if CoverageFormat2 has unsorted ranges, bail out.
Otherwise, 64k ranges of each 64k glyphs can DoS closure() method.

We can do the same for CoverageFormat1, but that one does not expose
the quadratic behavior, so, fine.

With this hb-view/hb-shape support pipes and possibly socket and named pipe
also, anything fails just on mmap.

We can later do the same for Windows also.

This however reveals two issues, the fact most of our bots don't have HAVE_MMAP and using
this instead the other fread/fopen reader can make failure on CI. I should look at them separately
this change however is very low risk I believe.

As https://github.com/harfbuzz/harfbuzz/pull/1059#issuecomment-397912812 we
like to still work with blobs that harfbuzz itself can't handle directly that are failing sanitization
currently apparently.

This checks if the blob isn't empty and uses `hb_face_count`
to see if the font file passes the simple font file sanitization
so can detect if the input is actually a font and checks also
whether input font-index is out of range.

We were passing the font path directly to freetype so rendering
was broken when we are getting the font from stdin.

This fixes it by using FT_New_Memory_Face instead.

This fixes:
* build/util/hb-view /dev/stdin text < font.ttf
* build/util/hb-view - text < font.ttf
* cat font.ttf | build/util/hb-view - text

but doesn't work on
* cat font.ttf | build/util/hb-view /dev/stdin text

which I will try to fix separately.