1, Use #if defined() to judge the switching macro such as compiler macro.

1, Use #if defined() to judge the switching macro such as compiler macro.
Original, some code directly judge the value of these macros, but linux ICC compiler will report error as "zero used for undefined preprocessing identifier". So it is better judge whether these macros are defined before accessing their value.
2, Use #if defined() style to replace #ifdef style.
It is good to keep consistent style for this case.

git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@7597 6f19259b-4bc3-4df7-8a09-765794883524