Improve macro hygiene

This commit improves hygiene and formatting of macro definitions
throughout the library. Specifically:
- It adds brackets around parameters to avoid unintended
  interpretation of arguments, e.g. due to operator precedence.
- It adds uses of the `do { ... } while( 0 )` idiom for macros that
  can be used as commands.

include/mbedtls/bignum.h

@@ -46,7 +46,12 @@
 #define MBEDTLS_ERR_MPI_NOT_ACCEPTABLE                    -0x000E  /**< The input arguments are not acceptable. */
 #define MBEDTLS_ERR_MPI_ALLOC_FAILED                      -0x0010  /**< Memory allocation failed. */
 
-#define MBEDTLS_MPI_CHK(f) do { if( ( ret = f ) != 0 ) goto cleanup; } while( 0 )
+#define MBEDTLS_MPI_CHK(f)       \
+    do                           \
+    {                            \
+        if( ( ret = (f) ) != 0 ) \
+            goto cleanup;        \
+    } while( 0 )
 
 /*
  * Maximum size MPIs are allowed to grow to in number of limbs.