needed for PKEY_DISABLE_WRITE. these are documented as also being from sys/
mman.h with GNU_SOURCE, but musl doesn't do that, so these are strictly from
kernel headers
--- a/base/allocator/partition_allocator/src/partition_alloc/partition_alloc_unittest.cc
+++ b/base/allocator/partition_allocator/src/partition_alloc/partition_alloc_unittest.cc
@@ -60,6 +60,7 @@
 #include <sys/mman.h>
 #include <sys/resource.h>
 #include <sys/time.h>
+#include <linux/mman.h>
 #endif  // BUILDFLAG(IS_POSIX)
 
 #if BUILDFLAG(ENABLE_PARTITION_ALLOC_AS_MALLOC_SUPPORT) && BUILDFLAG(IS_MAC)