libglvnd: work around crashing on musl systems and multithreaded gl

firstly, disable ppc64 tsb assembly since it appears to be broken
in multithread contexts; secondly, when not using asm, compile the
dispatch code with low optimization level as doing otherwise seems
to result in crashes in multithreaded contexts

we'll need to fix this properly at some point, for now do this

the assembly code is seemingly buggy and causes strange crashes
when used with threaded code, so fall back to pure C paths

srcpkgs/libglvnd/patches/musl-noasm-use-o0.patch

@@ -0,0 +1,52 @@
+From d82adbb78a246d68d67a951cdfc81b757fac2453 Mon Sep 17 00:00:00 2001
+From: Daniel Kolesa <daniel@octaforge.org>
+Date: Mon, 10 May 2021 23:02:21 +0200
+Subject: [PATCH] lower optimization for dispatch code when using C + tsb
+
+there appears to be some bug in the code which causes crashes
+with threaded opengl setups; this manifests at least on ppc64(le)
+with musl (where one must set `-Dtls=enabled`). I haven't been
+able to track it down yet, but this workaround at least makes it
+stop happening.
+---
+ src/GLdispatch/vnd-glapi/meson.build | 8 ++++++--
+ 1 file changed, 6 insertions(+), 2 deletions(-)
+
+diff --git src/GLdispatch/vnd-glapi/meson.build src/GLdispatch/vnd-glapi/meson.build
+index 615cdff..94310b3 100644
+--- src/GLdispatch/vnd-glapi/meson.build
++++ src/GLdispatch/vnd-glapi/meson.build
+@@ -35,8 +35,12 @@ else
+ endif
+ 
+ _entry_files = []
++_extra_cflags = []
+ if gl_dispatch_type == 'pure_c'
+   _entry_files += 'entry_pure_c.c'
++  if not have_tls
++    _extra_cflags += '-O0'
++  endif
+ else
+   _entry_files += 'entry_common.c'
+   if gl_dispatch_type != 'armv7_tsd'
+@@ -73,7 +77,7 @@ libglapi = static_library(
+     glapi_mapi_tmp_h,
+     _entry_files,
+   ],
+-  c_args : ['-DMAPI_ABI_HEADER="@0@"'.format(glapi_mapi_tmp_h.full_path())],
++  c_args : ['-DMAPI_ABI_HEADER="@0@"'.format(glapi_mapi_tmp_h.full_path())] + _extra_cflags,
+   include_directories : inc_include,
+   dependencies : idep_utils_misc,
+   gnu_symbol_visibility : 'hidden',
+@@ -89,7 +93,7 @@ foreach g : ['gl', 'opengl', 'glesv1', 'glesv2']
+     c_args : [
+       '-DSTATIC_DISPATCH_ONLY',
+       '-DMAPI_ABI_HEADER="@0@"'.format(header.full_path()),
+-    ],
++    ] + _extra_cflags,
+     include_directories : [inc_include, inc_util],
+     gnu_symbol_visibility : 'hidden',
+   )
+-- 
+2.31.1
+

srcpkgs/libglvnd/template

@@ -1,7 +1,7 @@
 # Template file for 'libglvnd'
 pkgname=libglvnd
 version=1.3.2
-revision=1
+revision=2
 wrksrc="libglvnd-v${version}"
 build_style=meson
 hostmakedepends="pkg-config"
@@ -21,7 +21,10 @@ if [ "$XBPS_TARGET_LIBC" = "musl" ]; then
 	configure_args="-Dtls=disabled"
 fi
 
+# ppc64_tsd (used when ppc64_tls is not available)
+# is broken with threads, so disable it on musl
 case "$XBPS_TARGET_MACHINE" in
+	ppc*-musl) configure_args+=" -Dasm=disabled";;
 	ppc64*) ;;
 	arm*|mips*|ppc*) configure_args+=" -Dasm=disabled";;
 esac