[1.10.x] Fix pthread use on FreeBSD (#253) (#262)

Much like OpenBSD, the FreeBSD pthread APIs are not imported with the
appropriate nullability annotations, so the base pthread mutex type
should be an optional value. Eventually we should provide API notes to
fix this issue, but that is not in place today.
See swiftlang/swift#81407

(cherry picked from commit 9d7ff77)

Co-authored-by: Evan Wilde <[email protected]>

Author: simonjbeaumont

Sources/X509/Lock.swift

@@ -35,7 +35,7 @@ import wasi_pthread
 #if os(Windows)
 @usableFromInline
 typealias LockPrimitive = SRWLOCK
-#elseif os(OpenBSD)
+#elseif os(OpenBSD) || os(FreeBSD)
 @usableFromInline
 typealias LockPrimitive = pthread_mutex_t?
 #else
@@ -54,14 +54,14 @@ extension LockOperations {
         #if os(Windows)
         InitializeSRWLock(mutex)
         #elseif (compiler(<6.1) && !os(WASI)) || (compiler(>=6.1) && _runtime(_multithreaded))
-        #if os(OpenBSD)
+        #if os(OpenBSD) || os(FreeBSD)
         var attr = pthread_mutexattr_t(bitPattern: 0)
         #else
         var attr = pthread_mutexattr_t()
         #endif
         pthread_mutexattr_init(&attr)
         debugOnly {
-            #if os(OpenBSD)
+            #if os(OpenBSD) || os(FreeBSD)
             pthread_mutexattr_settype(&attr, .init(PTHREAD_MUTEX_ERRORCHECK.rawValue))
             #else
             pthread_mutexattr_settype(&attr, .init(PTHREAD_MUTEX_ERRORCHECK))