pkg-config issue on macOS with builtin pkgs in OSX_SDK_PATH

[Tobias Nygren <tnn%NetBSD.org@localhost>]

Hi,

I have found that builtin package handling on macOS isn't fully aware
of OSX_SDK_PATH. When generating pkg-config files it sets the prefix
in the .pc file to /usr. This can lead to issues with some packages
that actually stat $prefix/include to see if it exists.
At least zlib and editline suffer from this problem, with for example
x11/qt6-qtbase failing like this due to zlib:

CMake Error in src/gui/CMakeLists.txt:
  Imported target "WrapHarfbuzz::WrapHarfbuzz" includes non-existent path
    "/usr/include"

Also, math/nickle fails to detect builtin editline correctly.

I would like to propose the following patch for this issue.
Don't have the hardware to do a full bulk build but I'm running
a pkgrrx of ~900 packages and will wait for it to finish before
committing anything.

Index: mk/buildlink3/bsd.buildlink3.mk
===================================================================
RCS file: /cvsroot/pkgsrc/mk/buildlink3/bsd.buildlink3.mk,v
retrieving revision 1.265
diff -p -u -r1.265 bsd.buildlink3.mk
--- mk/buildlink3/bsd.buildlink3.mk	11 Oct 2024 12:18:07 -0000	1.265
+++ mk/buildlink3/bsd.buildlink3.mk	1 May 2025 11:21:45 -0000
@@ -424,8 +424,10 @@ USE_BUILTIN.${_pkg_}?=		no
 _BLNK_PKG_DBDIR.${_pkg_}?=	_BLNK_PKG_DBDIR.${_pkg_}_not_found
 _BLNK_PKG_INFO.${_pkg_}?=	${TRUE}
 BUILDLINK_PKGNAME.${_pkg_}?=	${_pkg_}
+.    if defined(OSX_SDK_PATH)
+BUILDLINK_PREFIX.${_pkg_}?=	${OSX_SDK_PATH}/usr
 # Usual systems has builtin packages in /usr
-.    if exists(${TOOLS_CROSS_DESTDIR}/usr)
+.    elif exists(${TOOLS_CROSS_DESTDIR}/usr)
 BUILDLINK_PREFIX.${_pkg_}?=	/usr
 # Haiku OS has posix packages in /boot/sytem/develop (or /boot/common)
 .    elif exists(${TOOLS_CROSS_DESTDIR}/boot/system/develop)

Kind regards,
-Tobias