clang-format: Don't adapt local format to macros.

Formatting this:
   void f() { // 1 space initial indent.
      int i;
  #define A   \
      int i;  \
     int j;
        int k; // Format this line.
   }
   void f() {
       #define A 1 // Format this line.
   }

Before:
   void f() { // 1 space initial indent.
      int i;
  #define A   \
      int i;  \
     int j;
     int k;  // Format this line.
   }
   void f() {
   #define A 1  // Format this line.
   }

After:
   void f() { // 1 space initial indent.
      int i;
  #define A   \
      int i;  \
     int j;
      int k;  // Format this line.
   }
   void f() {
  #define A 1  // Format this line.
   }