net: dedup MSG_NOSIGNAL and MSG_DONTWAIT definitions

Summary:
Deduplicate `MSG_NOSIGNAL` and `MSG_DONTWAIT` definitions from `net.cpp`
and `netbase.cpp` to `compat.h` where they can also be reused by other
code.

This is a backport of [[bitcoin/bitcoin#20685 | [[bitcoin/bitcoin#20685 | core#20685]]]] [10/20]
bitcoin/bitcoin@78fdfbe

Depends on D11018

Test Plan:
`ninja all check-all`

eviewers:

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D11019

src/compat.h

@@ -98,4 +98,16 @@ static bool inline IsSelectableSocket(const SOCKET &s) {
 #endif
 }
 
+// MSG_NOSIGNAL is not available on some platforms, if it doesn't exist define
+// it as 0
+#if !defined(MSG_NOSIGNAL)
+#define MSG_NOSIGNAL 0
+#endif
+
+// MSG_DONTWAIT is not available on some platforms, if it doesn't exist define
+// it as 0
+#if !defined(MSG_DONTWAIT)
+#define MSG_DONTWAIT 0
+#endif
+
 #endif // BITCOIN_COMPAT_H

src/net.cpp

@@ -12,6 +12,7 @@
 #include <avalanche/avalanche.h>
 #include <banman.h>
 #include <clientversion.h>
+#include <compat.h>
 #include <config.h>
 #include <consensus/consensus.h>
 #include <crypto/sha256.h>
@@ -92,18 +93,6 @@ static constexpr std::chrono::seconds MAX_UPLOAD_TIMEFRAME{60 * 60 * 24};
 // synchronization.
 #define FEELER_SLEEP_WINDOW 1
 
-// MSG_NOSIGNAL is not available on some platforms, if it doesn't exist define
-// it as 0
-#if !defined(MSG_NOSIGNAL)
-#define MSG_NOSIGNAL 0
-#endif
-
-// MSG_DONTWAIT is not available on some platforms, if it doesn't exist define
-// it as 0
-#if !defined(MSG_DONTWAIT)
-#define MSG_DONTWAIT 0
-#endif
-
 /** Used to pass flags to the Bind() function */
 enum BindFlags {
     BF_NONE = 0,

src/netbase.cpp

@@ -5,6 +5,7 @@
 
 #include <netbase.h>
 
+#include <compat.h>
 #include <sync.h>
 #include <tinyformat.h>
 #include <util/sock.h>
@@ -29,10 +30,6 @@
 #include <poll.h>
 #endif
 
-#if !defined(MSG_NOSIGNAL)
-#define MSG_NOSIGNAL 0
-#endif
-
 // Settings
 static Mutex g_proxyinfo_mutex;
 static proxyType proxyInfo[NET_MAX] GUARDED_BY(g_proxyinfo_mutex);