Pass CommonJdkFlags to errorprone builds, which is required for
frameworks/base/layoutlib/create to work correctly. Unfortunately,
javac and errorprone cannot use the same syntax for the heap size,
javac needs -J-Xmx and errorprone needs -Xmx, so split the heap size
flag out into a separate variable.
Test: m -j RUN_ERROR_PRONE=true javac-check
Change-Id: Icd7f8cf627534fb089ec83e462c060572dd2d20c