[clang-tidy] Add noexcept where move is used

Found with performance-noexcept-move-constructor
Signed-off-by: Rosen Penev <rosenp@gmail.com>

include/fmt/format.h

@@ -607,14 +607,14 @@ class basic_memory_buffer : private Allocator, public internal::buffer<T> {
     of the other object to it.
     \endrst
    */
-  basic_memory_buffer(basic_memory_buffer&& other) { move(other); }
+  basic_memory_buffer(basic_memory_buffer&& other) FMT_NOEXCEPT { move(other); }
 
   /**
     \rst
     Moves the content of the other ``basic_memory_buffer`` object to this one.
     \endrst
    */
-  basic_memory_buffer& operator=(basic_memory_buffer&& other) {
+  basic_memory_buffer& operator=(basic_memory_buffer&& other) FMT_NOEXCEPT {
     assert(this != &other);
     deallocate();
     move(other);

include/fmt/posix.h

@@ -146,7 +146,7 @@ class buffered_file {
     other.file_ = nullptr;
   }
 
-  buffered_file& operator=(buffered_file&& other) {
+  buffered_file& operator=(buffered_file&& other) FMT_NOEXCEPT {
     close();
     file_ = other.file_;
     other.file_ = nullptr;
@@ -209,7 +209,7 @@ class file {
 
   file(file&& other) FMT_NOEXCEPT : fd_(other.fd_) { other.fd_ = -1; }
 
-  file& operator=(file&& other) {
+  file& operator=(file&& other) FMT_NOEXCEPT {
     close();
     fd_ = other.fd_;
     other.fd_ = -1;