Add -Wno-unknown-pragmas (#7291)

diff --git a/setup.py b/setup.py
index cb5c341..67d2ea0 100644
--- a/setup.py
+++ b/setup.py
@@ -533,6 +533,7 @@
         '-Wno-missing-field-initializers',
         '-Wno-write-strings',
         '-Wno-zero-length-array',
+        '-Wno-unknown-pragmas',
         # This is required for Python 2 declarations that are deprecated in 3.
         '-Wno-deprecated-declarations',
         # Python 2.6 requires -fno-strict-aliasing, see