network: fix strerror_r detection for musl

/home/thomas/br-test-pkg/bootlin-armv7-musl/build/fluent-bit-4.0.8/src/flb_network.c: In function ‘net_connect_async’:
/home/thomas/br-test-pkg/bootlin-armv7-musl/build/fluent-bit-4.0.8/src/flb_network.c:653:17: error: assignment to ‘char *’ from ‘int’ makes pointer from integer without a cast [-Wint-conversion]
  653 |             str = strerror_r(error, so_error_buf, sizeof(so_error_buf));
      |                 ^

This fix should work perfectly for:

glibc systems: Uses str = strerror_r(...) (GNU version)
musl systems: Uses ret = strerror_r(...); if (ret == 0) str = so_error_buf; (POSIX version)
Other libc implementations: Defaults to POSIX behavior

Fix is similar to janet-lang/janet@a5d6b22.

Signed-off-by: Thomas Devoogdt <[email protected]>

Author: ThomasDevoogdt

src/flb_network.c

@@ -638,9 +638,9 @@ static int net_connect_async(int fd,
             }
 
             /* Connection is broken, not much to do here */
-#if ((defined(_POSIX_C_SOURCE) && _POSIX_C_SOURCE >= 200112L) ||    \
-     (defined(_XOPEN_SOURCE) || _XOPEN_SOURCE - 0L >= 600L)) &&     \
-  (!defined(_GNU_SOURCE))
+#ifdef __GLIBC__
+            str = strerror_r(error, so_error_buf, sizeof(so_error_buf));
+#else
             ret = strerror_r(error, so_error_buf, sizeof(so_error_buf));
             if (ret == 0) {
                 str = so_error_buf;
@@ -649,8 +649,6 @@ static int net_connect_async(int fd,
                 flb_errno();
                 return -1;
             }
-#else
-            str = strerror_r(error, so_error_buf, sizeof(so_error_buf));
 #endif
             flb_error("[net] TCP connection failed: %s:%i (%s)",
                       u->tcp_host, u->tcp_port, str);