Catch std::bad_alloc by reference

GCC 8.1.1 complains when catching by value due to polymorphism.

Signed-off-by: Nathaniel McCallum <npmccallum@redhat.com>

sdk/protected_fs/sgx_tprotected_fs/file_read_write.cpp

@@ -425,7 +425,7 @@ file_data_node_t* protected_fs_file::append_data_node()
 	try {
 		new_file_data_node = new file_data_node_t;
 	}
-	catch (std::bad_alloc e) {
+	catch (std::bad_alloc& e) {
 		(void)e; // remove warning
 		last_error = ENOMEM;
 		return NULL;
@@ -471,7 +471,7 @@ file_data_node_t* protected_fs_file::read_data_node()
 	try {
 		file_data_node = new file_data_node_t;
 	}
-	catch (std::bad_alloc e) {
+	catch (std::bad_alloc& e) {
 		(void)e; // remove warning
 		last_error = ENOMEM;
 		return NULL;
@@ -563,7 +563,7 @@ file_mht_node_t* protected_fs_file::append_mht_node(uint64_t mht_node_number)
 	try {
 		new_file_mht_node = new file_mht_node_t;
 	}
-	catch (std::bad_alloc e) {
+	catch (std::bad_alloc& e) {
 		(void)e; // remove warning
 		last_error = ENOMEM;
 		return NULL;
@@ -609,7 +609,7 @@ file_mht_node_t* protected_fs_file::read_mht_node(uint64_t mht_node_number)
 	try {
 		file_mht_node = new file_mht_node_t;
 	}
-	catch (std::bad_alloc e) {
+	catch (std::bad_alloc& e) {
 		(void)e; // remove warning
 		last_error = ENOMEM;
 		return NULL;

sdk/protected_fs/sgx_tprotected_fs/lru_cache.cpp

@@ -76,7 +76,7 @@ bool lru_cache::add(uint64_t key, void* data)
 		map_node = new map_node_t();
 		list_node = new list_node_t();
 	}
-	catch (std::bad_alloc e) {
+	catch (std::bad_alloc& e) {
 		(void)e; // remove warning
 		return false;
 	}
@@ -131,7 +131,7 @@ void* lru_cache::get(uint64_t key)
 			list_node = new list_node_t();
 			list_node->key = map_it->first;
 		}
-		catch (std::bad_alloc e) {
+		catch (std::bad_alloc& e) {
 			(void)e; // remove warning
 			return NULL;
 		}

sdk/protected_fs/sgx_tprotected_fs/sgx_tprotected_fs.cpp

@@ -49,7 +49,7 @@ static SGX_FILE* sgx_fopen_internal(const char* filename, const char* mode, cons
 	try {
 		file = new protected_fs_file(filename, mode, auto_key, kdk_key);
 	}
-	catch (std::bad_alloc e) {
+	catch (std::bad_alloc& e) {
 		(void)e; // remove warning
 		errno = ENOMEM;
 		return NULL;