build: fix build and provide compat for OpenBSD

- wayland-egl-abi-check: try to use llvm-nm first instead of BSD nm (incompatible options)
- avoid forcing _POSIX_C_SOURCE=200809L (SOCK_CLOEXEC become available)
- epoll(7) is provided by a userspace wrapper around kqueue(2) as FreeBSD
- when using SO_PEERCRED, the struct to use is `struct sockpeercred` instead of `struct ucred` on OpenBSD
- provide a compatibility layer for count_open_fds() using sysctl(2) as FreeBSD

Signed-off-by: Sebastien Marie <semarie@online.fr>

tests/test-helpers.c

@@ -61,6 +61,33 @@ count_open_fds(void)
 	assert(error == 0 && "sysctl KERN_PROC_NFDS failed.");
 	return nfds;
 }
+#elif defined(__OpenBSD__)
+#include <sys/sysctl.h>
+
+/*
+ * On OpenBSD, get file descriptor information using sysctl()
+ */
+int
+count_open_fds(void)
+{
+	int error;
+	int mib[6];
+	size_t size;
+
+	mib[0] = CTL_KERN;
+	mib[1] = KERN_FILE;
+	mib[2] = KERN_FILE_BYPID;
+	mib[3] = getpid();
+	mib[4] = sizeof(struct kinfo_file);
+	mib[5] = 0;
+
+	/* find the size required to store all the entries */
+	error = sysctl(mib, 6, NULL, &size, NULL, 0);
+	assert(error != -1 && "sysctl KERN_FILE_BYPID failed.");
+
+	/* return the current number of entries */
+	return size / sizeof(struct kinfo_file);
+}
 #else
 int
 count_open_fds(void)

tests/test-runner.c

@@ -308,6 +308,13 @@ is_debugger_attached(void)
 
 	return rc;
 }
+#else
+static int
+is_debugger_attached(void)
+{
+	/* 0=debugger can't be determined */
+	return 0;
+}
 #endif
 
 int main(int argc, char *argv[])