Previously the CHECK_HEADER_ADD_INCLUDE function defined the
`HAVE_<header>_H` preprocessor macros to value 0 or 1 whether the
`<header.h>` file was found. This syncs it with Autotools build system
where most of these macros are either undefined or defined to 1.
In possible edge cases where such macros might be intentionally used
like this without being aware that HAVE_HEADER_H can be 0 or 1 on
Windows:
| #ifdef HAVE_HEADER_H
| ...
| #endif
there is backwards incompatibility for PECL extensions in case the
header wouldn't exist on Windows such code wouldn't execute. However,
this is considered a bug if such case is present. From the Autotools
point of view, the check is correct though and should be used with
ifdef/defined() checks.
Help text is also synced to Autotools style:
`Define to 1 if you have the <header.h> header file.`
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