build: adjust linking for Crypto (#137)

The package DLL `Crypto.dll` was building the BoringSSL wrapper
(`CryptoBoringWrapper`) in the style that the user requested (static or
shared).  However, there is a single user of the library and is not
directly included by the SPM client.  Furthermore, the library was not
setup for installation which makes redistribution of it impossible.
Always build the library in a static mode to allow compaction into the
`Crypto` target.

Sources/CryptoBoringWrapper/CMakeLists.txt

@@ -12,7 +12,7 @@
 ##
 ##===----------------------------------------------------------------------===##
 
-add_library(CryptoBoringWrapper
+add_library(CryptoBoringWrapper STATIC
   "AEAD/BoringSSLAEAD.swift"
   "CryptoKitErrors_boring.swift")