win+Meson: allow for xdiff to be compiled with MSVC

The `build_rust.sh` script is quite opinionated about the naming scheme
of the C compiler: It assumes that the xdiff library file will be named
`libxdiff.a`.

However, MS Visual C generates `xdiff.lib` files instead; This naming
scheme has been in use in a very, very long time.

Let's allow for that.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Author: dscho

build_rust.sh

@@ -44,7 +44,12 @@ fi
 
 cd $dir_rust && cargo clean && pwd && cargo build -p $crate $rust_args; cd ..
 
-libfile="lib${crate}.a"
+if grep x86_64-pc-windows-msvc rust/target/.rustc_info.json
+then
+  libfile="${crate}.lib"
+else
+  libfile="lib${crate}.a"
+fi
 dst=$dir_build/$libfile
 
 if [ "$dir_git_root" != "$dir_build" ]; then

meson.build

@@ -277,8 +277,16 @@ else
   rustflags = '-Aunused_imports -Adead_code -C debuginfo=2 -C opt-level=1 -C force-frame-pointers=yes'
 endif
 
+compiler = meson.get_compiler('c')
+
+if compiler.get_id() == 'msvc'
+  xdiff_lib_filename = 'xdiff.lib'
+else
+  xdiff_lib_filename = 'libxdiff.a'
+endif
+
 rust_build_xdiff = custom_target('rust_build_xdiff',
-  output: 'libxdiff.a',
+  output: xdiff_lib_filename,
   build_by_default: true,
   build_always_stale: true,
   command: [
@@ -288,8 +296,6 @@ rust_build_xdiff = custom_target('rust_build_xdiff',
   install: false,
 )
 
-compiler = meson.get_compiler('c')
-
 libgit_sources = [
   'abspath.c',
   'add-interactive.c',