fluent-bit: Fix musl strerror_r behavior

Musl now seems to default to POSIX strerror_r, so we
need to fix the function accordingly. Patch pulled from
upstream 5ab8f149eeb2b4df596250a926eb6a39e373a834.

fluent-bit/patches/0021-network-fix-strerror_r-detection-for-musl.patch

@@ -0,0 +1,55 @@
+From 5ab8f149eeb2b4df596250a926eb6a39e373a834 Mon Sep 17 00:00:00 2001
+From: Thomas Devoogdt <thomas@devoogdt.com>
+Date: Sun, 31 Aug 2025 16:05:25 +0200
+Subject: [PATCH] network: fix strerror_r detection for musl
+MIME-Version: 1.0
+Content-Type: text/plain; charset=UTF-8
+Content-Transfer-Encoding: 8bit
+
+/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 https://github.com/janet-lang/janet/commit/a5d6b2283834422a9fa9e79b5c7ad9b932b52568.
+
+Signed-off-by: Thomas Devoogdt <thomas@devoogdt.com>
+---
+ src/flb_network.c | 8 +++-----
+ 1 file changed, 3 insertions(+), 5 deletions(-)
+
+diff --git a/src/flb_network.c b/src/flb_network.c
+index 4caad9ef1..5d6937ca7 100644
+--- a/src/flb_network.c
++++ b/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);
+-- 
+2.52.0
+