Build failure with GCC 14 - implicit decl. of scm_c_issue_deprecation_warning_fmt

[Kacper Słomiński]

Trying to build guile-reader with GCC 14 causes the build to fail due to 
the following error:

libtool: compile:  x86_64-pc-linux-gnu-gcc -DHAVE_CONFIG_H -I. -I.. -I. 
-I. -I.. -I/usr/include/guile/3.0 -Winline -Wdeclaration-after-statement 
-Wcast-align -Wpointer-arith -Wall -O3 -march=znver2 -pipe -ggdb3 -c 
compat.c  -fPIC -DPIC -o .libs/compat.o
compat.c: In function ‘tag_to_type’:
compat.c:241:9: error: implicit declaration of function 
‘scm_c_issue_deprecation_warning_fmt’ [-Wimplicit-function-declaration]
  241 |         scm_c_issue_deprecation_warning_fmt
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

This used to just be a warning, but as of GCC 14 (and Clang 17) is 
treated as an error, because C99 disallows it, and compilers have 
started enforcing it.

I've had a cursory look, and it seems that the function in question is 
provided by "libguile/deprecation.h", which is not included by any 
top-level libguile header. This seems to be the case for both Guile 2.2 
and Guile 3.0. I'm not sure what it's like in Guile 1.8 though, so I 
don't know whether just adding the missing include is the correct fix.

For reference, here's the Gentoo bug report for this: 
https://bugs.gentoo.org/874384.