Add patch (#8034)

var/spack/repos/builtin/packages/pixman/clang.patch

@@ -0,0 +1,28 @@
+--- pixman-0.34.0/test/utils-prng.c.bak	2018-02-01 00:34:15.757691302 +0100
++++ pixman-0.34.0/test/utils-prng.c	2018-02-01 00:36:38.285690995 +0100
+@@ -199,12 +199,24 @@
+         }
+         else
+         {
++
++#ifndef __has_builtin
++#define __has_builtin(x) 0
++#endif
++
+ #ifdef HAVE_GCC_VECTOR_EXTENSIONS
++# if !defined(__clang__) || __has_builtin(__builtin_shuffle)
+             const uint8x16 bswap_shufflemask =
+             {
+                 3, 2, 1, 0, 7, 6, 5, 4, 11, 10, 9, 8, 15, 14, 13, 12
+             };
+             randdata.vb = __builtin_shuffle (randdata.vb, bswap_shufflemask);
++# elif __has_builtin(__builtin_shufflevector)
++            randdata.vb = __builtin_shufflevector(randdata.vb, randdata.vb, 3, 2, 1, 0, 7, 6, 5, 4, 11, 10, 9, 8, 15, 14, 13, 12);
++# else
++#  error "GCC_VECTOR_EXTENSION is defined, but neither __builtin_shuffle nor __builtin_shufflevector is supported!"
++# endif
++
+             store_rand_128_data (buf, &randdata, aligned);
+             buf += 16;
+ #else
+

var/spack/repos/builtin/packages/pixman/package.py

@@ -40,6 +40,13 @@ class Pixman(AutotoolsPackage):
     depends_on('pkgconfig', type='build')
     depends_on('libpng')
 
+    # As discussed here:
+    # https://bugs.freedesktop.org/show_bug.cgi?id=104886
+    # __builtin_shuffle was removed in clang 5.0.
+    # From version 9.1 apple-clang is based on clang 5.0.
+    # Patch is obtained from above link.
+    patch('clang.patch', when='%clang@9.1.0-apple:')
+
     def configure_args(self):
         args = [
             '--enable-libpng',