test: Remove uses of O_TMPFILE

`O_TMPFILE` requires file system support, which may not be available in
certain environments, usually containerized ones. So do not use it.

A new function is added for tests to be able to create unnamed temporary
files using `libcamera::MemFd` as the implementation.

Signed-off-by: Barnabás Pőcze <barnabas.pocze@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Paul Elder <paul.elder@ideasonboard.com>

test/log/log_api.cpp

@@ -109,18 +109,17 @@ protected:
 
 	int testFile()
 	{
-		int fd = open("/tmp", O_TMPFILE | O_RDWR, S_IRUSR | S_IWUSR);
-		if (fd < 0) {
+		UniqueFD fd = test::createTemporaryFile();
+		if (!fd.isValid()) {
 			cerr << "Failed to open tmp log file" << endl;
 			return TestFail;
 		}
 
 		char path[32];
-		snprintf(path, sizeof(path), "/proc/self/fd/%u", fd);
+		snprintf(path, sizeof(path), "/proc/self/fd/%u", fd.get());
 
 		if (logSetFile(path) < 0) {
 			cerr << "Failed to set log file" << endl;
-			close(fd);
 			return TestFail;
 		}
 
@@ -128,13 +127,11 @@ protected:
 
 		char buf[1000];
 		memset(buf, 0, sizeof(buf));
-		lseek(fd, 0, SEEK_SET);
-		if (read(fd, buf, sizeof(buf)) < 0) {
+		lseek(fd.get(), 0, SEEK_SET);
+		if (read(fd.get(), buf, sizeof(buf)) < 0) {
 			cerr << "Failed to read tmp log file" << endl;
-			close(fd);
 			return TestFail;
 		}
-		close(fd);
 
 		istringstream iss(buf);
 		return verifyOutput(iss);