I tested on smoke/preR13 and work/preR13 branches

```
$ make distclean
$ ./configure --disable-write
$ make
```

Error:
```
...
  CCLD     dwgread
/usr/bin/ld: ../src/.libs/libredwg.so: undefined reference to `dwg_add_LAYER'
/usr/bin/ld: ../src/.libs/libredwg.so: undefined reference to `dwg_add_STYLE'
/usr/bin/ld: ../src/.libs/libredwg.so: undefined reference to `dwg_add_APPID'
/usr/bin/ld: ../src/.libs/libredwg.so: undefined reference to `dwg_add_LTYPE'
/usr/bin/ld: ../src/.libs/libredwg.so: undefined reference to `dwg_add_VIEW'
/usr/bin/ld: ../src/.libs/libredwg.so: undefined reference to `dwg_add_DIMSTYLE'
/usr/bin/ld: ../src/.libs/libredwg.so: undefined reference to `dwg_add_VPORT'
/usr/bin/ld: ../src/.libs/libredwg.so: undefined reference to `dwg_add_BLOCK_HEADER'
/usr/bin/ld: ../src/.libs/libredwg.so: undefined reference to `dwg_add_Document'
collect2: error: ld returned 1 exit status
...
```
Cannot build libredwg with --disable-write
This is a GitHub Issue
repo:libredwg
owner:LibreDWG
Title : Cannot build libredwg with --disable-write
Issue date:

--- start body ---
I tested on smoke/preR13 and work/preR13 branches

```
$ make distclean
$ ./configure --disable-write
$ make
```

Error:
```
...
  CCLD     dwgread
/usr/bin/ld: ../src/.libs/libredwg.so: undefined reference to `dwg_add_LAYER'
/usr/bin/ld: ../src/.libs/libredwg.so: undefined reference to `dwg_add_STYLE'
/usr/bin/ld: ../src/.libs/libredwg.so: undefined reference to `dwg_add_APPID'
/usr/bin/ld: ../src/.libs/libredwg.so: undefined reference to `dwg_add_LTYPE'
/usr/bin/ld: ../src/.libs/libredwg.so: undefined reference to `dwg_add_VIEW'
/usr/bin/ld: ../src/.libs/libredwg.so: undefined reference to `dwg_add_DIMSTYLE'
/usr/bin/ld: ../src/.libs/libredwg.so: undefined reference to `dwg_add_VPORT'
/usr/bin/ld: ../src/.libs/libredwg.so: undefined reference to `dwg_add_BLOCK_HEADER'
/usr/bin/ld: ../src/.libs/libredwg.so: undefined reference to `dwg_add_Document'
collect2: error: ld returned 1 exit status
...
```
--- end body ---
