Sure, gcc knows to warn about this as well:

../../util/options.cc:175:17: warning: this statement may fall through [-Wimplicit-fallthrough=]
     case 1: m.r = m.t;
             ~~~~^~~~~
../../util/options.cc:176:5: note: here
     case 2: m.b = m.t;
     ^~~~

But HOLY SMOKES, look at clang -Weverything bot message:

options.cc:176:5: warning: unannotated fall-through between switch labels [-Wimplicit-fallthrough]
    case 2: m.b = m.t;
    ^
options.cc:176:5: note: insert 'HB_FALLTHROUGH;' to silence this warning
    case 2: m.b = m.t;
    ^
    HB_FALLTHROUGH;

Right, it's telling me to insert "HB_FALLTHROUGH;" there!!!!!!!!!

From clang -Weverything bot:

options.cc:39:3: warning: no previous extern declaration for non-static variable 'supported_font_funcs' [-Wmissing-variable-declarations]

From clang -Weverything bot:

./options.hh:57:8: warning: 'option_group_t' has virtual functions but non-virtual destructor [-Wnon-virtual-dtor]
struct option_group_t
       ^

Alternative woul have been to resurrect F_COMBINE that I removed in
70136a78

But this does it for now.  I'm not sure why check-static-inits.sh didn't
catch this before.  Clang -Weverything bot did:

  CXX      libharfbuzz_la-hb-ot-shape-complex-indic.lo
hb-ot-shape-complex-indic.cc:99:1: warning: declaration requires a global constructor [-Wglobal-constructors]
indic_features[] =
^
1 warning generated.
  CXX      libharfbuzz_la-hb-ot-shape-complex-khmer.lo
hb-ot-shape-complex-khmer.cc:36:1: warning: declaration requires a global constructor [-Wglobal-constructors]
khmer_features[] =
^
1 warning generated.

uint32_t was getting promoted to signed int, which is not what we wanted...

Wow, clang has become good at generating warnings...

../../src/hb-common.h:349:29: warning: signed shift result (0xFF000000) sets the sign bit of the shift expression's type ('int') and becomes negative [-Wshift-sign-overflow]
  _HB_SCRIPT_MAX_VALUE                          = HB_TAG_MAX, /*< skip >*/
                                                  ^~~~~~~~~~
../../src/hb-common.h:93:20: note: expanded from macro 'HB_TAG_MAX'
 define HB_TAG_MAX HB_TAG(0xff,0xff,0xff,0xff)
                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~
../../src/hb-common.h:89:57: note: expanded from macro 'HB_TAG'
 define HB_TAG(c1,c2,c3,c4) ((hb_tag_t)((((uint8_t)(c1))<<24)|(((uint8_t)(c2))<<16)|(((uint8_t)(c3))<<8)|((uint8_t)(c4))))
                                         ~~~~~~~~~~~~~~~^ ~~
../../src/hb-common.h:349:3: warning: ISO C restricts enumerator values to range of 'int' (4294967295 is too large) [-Wpedantic]
  _HB_SCRIPT_MAX_VALUE                          = HB_TAG_MAX, /*< skip >*/
  ^                                               ~~~~~~~~~~

And remove redundant implementations.

"Fixes" //github.com/harfbuzz/harfbuzz/issues/1191

#1196

Per https://github.com/Alexpux/MSYS2-packages/issues/163#issuecomment-73555971

As it may cause a race unrelated to the issue actually happened

As https://github.com/Alexpux/MSYS2-packages/issues/702

Using a hack...

text-rendering-tests test MORX-32 shows that for Insertion, an unset mark is treated
as mark set at 0.  This is unlike the Reordering lookup where un unset mark performs
nothing.

Fixes MORX-32.

Makes MORX-29, MORX-30, MORX-31 pass.

To help TSan.

A single find_package(harfbuzz) line in user code resulted in this loop
getting stuck when _harfbuzz_libdir_iter became "/".

See comment.