package/janet: fix build w/ musl

Since the commit [1] the janet package started failing on the
autobuilder when using musl libc:

```
[50/56] Compiling C object libjanet.so.1.35.2.p/meson-generated_.._janet.c.o
FAILED: libjanet.so.1.35.2.p/meson-generated_.._janet.c.o
/workdir/instance-0/output-1/host/bin/armeb-buildroot-linux-musleabi-gcc -Ilibjanet.so.1.35.2.p -I. -I.. -I../src/include -fdiagnostics-color=always -Wall -Winvalid-pch -std=c99 -O3 -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -O1 -g3 -fPIC -pthread -fvisibility=hidden -MD -MQ libjanet.so.1.35.2.p/meson-generated_.._janet.c.o -MF libjanet.so.1.35.2.p/meson-generated_.._janet.c.o.d -o libjanet.so.1.35.2.p/meson-generated_.._janet.c.o -c janet.c
src/core/util.c: In function 'janet_strerror':
src/core/util.c:977:12: error: returning 'int' from a function with return type 'const char *' makes pointer from integer without a cast [-Wint-conversion]
[51/56] Compiling C object janet-native.p/meson-generated_.._janet.c.o
```

The commit [2] introduced the issue in v1.35.0, the `strerror` function
has different definition on glibc compared to musl. This issue has been
addressed in commit [3]. This patch add the upstream commit [3].

[1] 31212c4c58 package/janet: bump to version 1.35.2
[2] 8334504f4e
[3] a5d6b22838

Fixes: https://autobuild.buildroot.org/results/ff1/ff1d6063c1a79d17cfa9910cca824e704a4a0c67/build-end.log
Signed-off-by: Thomas Perale <thomas.perale@mind.be>
Signed-off-by: Romain Naour <romain.naour@smile.fr>

package/janet/0001-check-for-glibc-instead-of-gnu-source.patch

@@ -0,0 +1,26 @@
+From a5d6b2283834422a9fa9e79b5c7ad9b932b52568 Mon Sep 17 00:00:00 2001
+From: Calvin Rose <calsrose@gmail.com>
+Date: Fri, 21 Jun 2024 17:17:22 -0500
+Subject: [PATCH] Check for __GLIBC__ instead of _GNU_SOURCE
+
+musl doesn't obey this behavior.
+
+Upstream: https://github.com/janet-lang/janet/commit/a5d6b2283834422a9fa9e79b5c7ad9b932b52568
+Signed-off-by: Thomas Perale <thomas.perale@mind.be>
+---
+ src/core/util.c | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+diff --git a/src/core/util.c b/src/core/util.c
+index 4bb37abc5..6cb5676e0 100644
+--- a/src/core/util.c
++++ b/src/core/util.c
+@@ -972,7 +972,7 @@ const char *janet_strerror(int e) {
+ #ifdef JANET_WINDOWS
+     /* Microsoft strerror seems sane here and is thread safe by default */
+     return strerror(e);
+-#elif defined(_GNU_SOURCE)
++#elif defined(__GLIBC__)
+     /* See https://linux.die.net/man/3/strerror_r */
+     return strerror_r(e, janet_vm.strerror_buf, sizeof(janet_vm.strerror_buf));
+ #else