fix: Fix Meson include directories

[WillAyd]

Quick follow up to https://github.com/apache/arrow-nanoarrow/pull/508 - the array.c includes stopped working without this

FAILED: libnanoarrow.so.p/src_nanoarrow_array.c.o 
ccache cc -Ilibnanoarrow.so.p -I. -I.. -fdiagnostics-color=always -D_FILE_OFFSET_BITS=64 -Wall -Winvalid-pch -Wextra -std=c99 -O0 -g -fPIC -MD -MQ libnanoarrow.so.p/src_nanoarrow_array.c.o -MF libnanoarrow.so.p/src_nanoarrow_array.c.o.d -o libnanoarrow.so.p/src_nanoarrow_array.c.o -c ../src/nanoarrow/array.c
../src/nanoarrow/array.c:23:10: fatal error: nanoarrow/nanoarrow.h: No such file or directory
   23 | #include "nanoarrow/nanoarrow.h"
      |          ^~~~~~~~~~~~~~~~~~~~~~~

[WillAyd]

I think the current issue has to do with the bundler - is the current bundling script supposed to replace the "nanoarrow/" prefix in the include?

[WillAyd]

Yea we could also have Meson generated the file in src/nanoarrow instead of just src, with the downside that we would then be allowing #include <nanoarrow.h> imports again instead of always forcing #include <nanoarrow/nanoarrow.h>

[paleolimbot]

Got it! Generating in the source directory is fine, I was just curious 🙂

[WillAyd]

Ah sorry - should have been clearer in my previous comment that I mean ${CMAKE_CURRENT_BINARY_DIR}/src/nanoarrow

Meson is super strict about where files can be generated. I'm not sure it would let you ever create something in the source directory, but if it did you'd be fighting against Meson to make it work. CMake is obviously a lot more relaxed, but I think it still makes sense to avoid generating anything in the source directory