refactor: Fix includes in crypto directory

IWYU issue #1763 appears to be a corner case, so it has been addressed
using a local pragma rather than a global mapping.

contrib/devtools/iwyu/bitcoin.core.imp

@@ -1,3 +1,11 @@
-# Nothing for now.
 [
+  # Compiler intrinsics.
+  # See: https://github.com/include-what-you-use/include-what-you-use/issues/1764.
+  { "include": [ "<emmintrin.h>", "private", "<immintrin.h>", "public" ] },
+  { "include": [ "<smmintrin.h>", "private", "<immintrin.h>", "public" ] },
+  { "include": [ "<tmmintrin.h>", "private", "<immintrin.h>", "public" ] },
+
+  # libc symbols.
+  { "symbol": ["AT_HWCAP", "private", "<sys/auxv.h>", "public"] },
+  { "symbol": ["AT_HWCAP2", "private", "<sys/auxv.h>", "public"] },
 ]