Upstream xapian-core uses lowercase xapian module.

**Describe the bug**



I've created a conan package for doxygen at conan-io/conan-center-index#2912.

(conan is a C/C++ package manager)



Conan provides packages for all dependencies.

It will also generate FindXXX cmake scripts for all dependencies, using the *official* names of upstream.

[xapian](https://xapian.org/download) ([download link](https://oligarchy.co.uk/xapian/1.4.17/xapian-core-1.4.17.tar.xz)) provides a `xapian-config.cmake` script.

This is downcase, while the FindXapian.cmake script in doxygen is capitalized.



By renaming `FindXapian.cmake` to `Findxapian.cmake` (=all lowercase), it is possible to override the module by the official one or the one created by conan (conan is able to generate FindXXX.cmake scripts).



This change is required to build doxygen with a static xapian library on all platforms.

A static xapian library requires extra system libraries, which the FindXapian.cmake script of doxygen does not provide (or detect).



Thanks!



**Expected behavior**

Configure + build succeeds



**To Reproduce**

Try to build doxygen and link to a static built xapian (used by doxysearch) on Linux.



```sh

# Run from the root of the doxygen source tree

python -m pip install --user conan

mkdir -p build_conan

cd build_conan

cat >conanfile.txt <<EOF

[requires]

xapian-core/1.4.16

[generators]

cmake

cmake_find_package

EOF

cat >CMakeLists.txt <<EOF

cmake_minimum_required(VERSION 3.1)

project(wrapper)

include("\${CMAKE_BINARY_DIR}/conanbuildinfo.cmake")

conan_basic_setup()

add_subdirectory(.. doxygen)

EOF

mkdir -p build

cd build

conan install ..

echo "set(XAPIAN_LIBRARIES \${xapian_LIBRARIES})" >>Findxapian.cmake   # Work around conan bug (it does not generate correct casings for variables)

cmake .. -Dbuild_search=ON -DCMAKE_MODULE_PATH=$PWD

cmake --build .

```



On current master, the following error occurs: (#8039 fixes this)



```

[ 99%] Linking CXX executable ../../../bin/doxysearch.cgi

/usr/bin/ld: /home/maarten/.conan/data/xapian-core/1.4.16/_/_/package/9a06a2acab1c746f80556aedd78e420138cb59ae/lib/libxapian.a(multimatch.o): in function `MultiMatch::get_mset(unsigned int, unsigned int, unsigned int, Xapian::MSet&, Xapian::Weight::Internal&, Xapian::MatchDecider const*, Xapian::KeyMaker const*)':

multimatch.cc:(.text+0x1212): undefined reference to `timer_delete'

/usr/bin/ld: multimatch.cc:(.text+0x136c): undefined reference to `timer_create'

/usr/bin/ld: multimatch.cc:(.text+0x13de): undefined reference to `timer_settime'

/usr/bin/ld: multimatch.cc:(.text+0x13f3): undefined reference to `timer_delete'

/usr/bin/ld: /home/maarten/.conan/data/xapian-core/1.4.16/_/_/package/9a06a2acab1c746f80556aedd78e420138cb59ae/lib/libxapian.a(multimatch.o): in function `MultiMatch::get_mset(unsigned int, unsigned int, unsigned int, Xapian::MSet&, Xapian::Weight::Internal&, Xapian::MatchDecider const*, Xapian::KeyMaker const*) [clone .cold]':

multimatch.cc:(.text.unlikely+0x403): undefined reference to `timer_delete'

/usr/bin/ld: /home/maarten/.conan/data/xapian-core/1.4.16/_/_/package/9a06a2acab1c746f80556aedd78e420138cb59ae/lib/libxapian.a(uuids.o): in function `Uuid::generate()':

uuids.cc:(.text+0x20): undefined reference to `uuid_generate'

collect2: error: ld returned 1 exit status

gmake[2]: *** [doxygen/addon/doxysearch/CMakeFiles/doxysearch.cgi.dir/build.make:106: bin/doxysearch.cgi] Error 1

gmake[1]: *** [CMakeFiles/Makefile2:661: doxygen/addon/doxysearch/CMakeFiles/doxysearch.cgi.dir/all] Error 2

gmake: *** [Makefile:172: all] Error 2

```







**Version**

Current master 0fc06d657d596adcc289a5f228973ea268efd66d





**Additional context**

Used (and tested) in https://github.com/conan-io/conan-center-index/pull/2912

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