Quote message in echo-error/echo-warning macros

Makes pretty-error and pretty-warning behave more like $(error) and
$(warning), where you don't need to do things like quote parentheses.

Bug: 118833208
Test: trigger the private_apis && sdk set error in sdk_check.mk,
      which no longer produces bash syntax errors

Change-Id: I766ff98ad4e652f59dbef9dd5654f1cd10a2d038