Hi

I've observed a regression in the generation of the Libs.private variable of sqlite3.pc. The @LDFLAGS_xxx@ content is not substituted. This breaks static linking scenarios.

Reproducer on Linux and MacOSX:
- wget https://www.sqlite.org/2025/sqlite-autoconf-3480000.tar.gz
- tar xvzf sqlite-autoconf-3480000.tar.gz
- cd sqlite-autoconf-3480000
- mkdir build
- cd build
- ../configure
- cat sqlite3.pc

outputs:
```
# Package Information for pkg-config

prefix=/usr/local
exec_prefix=${prefix}
libdir=${exec_prefix}/lib
includedir=${prefix}/include

Name: SQLite
Description: SQL database engine
Version: 3.48.0
Libs: -L${libdir} -lsqlite3
Libs.private: @LDFLAGS_MATH@ @LDFLAGS_ZLIB@ @LDFLAGS_ICU@
Cflags: -I${includedir}
```

Previous version 3.47.2 has instead: "Libs.private: -lz -lm -ldl -lpthread"