wrong pkgconfig content when cross compile with sysroot

[jacky-lau-1]

Describe the bug
I cross compile libcups with sysroot, I must use a CFLAGS with sysroot, otherwise configure will failed:

checking for inflateCopy in -lz... no
configure: error: Sorry, this software requires ZLIB 1.1 or higher.

I must use PKG_CONFIG_ALLOW_SYSTEM_LIBS=1, otherwise build will failed. But if I set the PKG_CONFIG_xxx environment variable, the cups3.pc has an unexpected content:

Lib.private: -L/tmp/mysysroot/usr/lib -lavahi-common -lavahi-client -lz -lm -lpthread

To Reproduce
Steps to reproduce the behavior:

1. Extract the tar file and enter the source directory
2. run ./configure --host=aarch64-linux-gnu
3. configure will failed
4. export CFLAGS="--sysroot=/tmp/mysysroot"
5. run ./configure --host=aarch64-linux-gnu
6. configure will successful and the cups3.pc don't have the unexpected content
7. run make, neither pdfio nor libcups can't find the depend libraries
8. export PKG_CONFIG_LIBDIR=/tmp/mysysrot/usr/lib/pkgconfig
9. export PKG_CONFIG_SYSROOT_DIR=/tmp/mysysroot
10. export PKG_CONFIG_ALLOW_SYSTEM_LIBS=1
11. run ./configure --host=aarch64-linux-gnu
12. configure will successful but the cups3.pc don't have the unexpected content
13. run make, both pdfio and libcups build sucessful.

Expected behavior
the cups3.pc shoud be:
Lib.private: -lavahi-common -lavahi-client -lz -lm -lpthread

System Information:

• OS: Ubuntu 22.04 LTS
• Version libcups3.0rc4

[michaelrsweet]

I suspect that pkg-config is including the library path; can you attach your config.log file?

[michaelrsweet]

@jacky-lau-1 Can you attach the config.log file?