add missing includes

[arkamar]

Several includes are missing based on linux man pages:

• strings.h for strcasecmp
• alloca.h for alloca
• stdio.h for fileno

The compilation with GCC 15 fails without those with implicit function declaration error.

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It is also worth to say that GCC 15 defaults to -std=c23, where bool is a reserved keyword, thus GCC produces following error:

src/H/bool.h:35:27: error: two or more data types in declaration specifiers
   35 |     typedef unsigned char bool;
      |                           ^~~~

I am using -std=c17 for now.