- Added a macro for checking clang compiler
 - Moved basic compiler checks to a macro
 - Added a macro for checking if compiler supports a flag
 - Added --enable-debug flag
 - Added a macro for running normal autoconf check with compiler flags
 - Added a macro for checking for verbose flag for different compilers (-Wall)
 - Added a macro for turning on strict standards compliance
 - Added a macro for turning warnings to errors
 - Added a macro for checking if compiler supports given pragma
 - Most of the flags now go through checks if the compilers supports them
   rather than enumerating different compilers
 - Added DSO symbol visibility for sun compiler
 - Enabled verbose mode for sun compiler
 - Fixed build for ICC 12.x by adding -wd279 to size_t checks
 - Removed pkg-config checks as those don't seem to be used anywhere
Signed-off-by: Mikko Koppanen <mkoppanen@php.net>