Well observed.

$ cat 832794.c
#include <iostream.h>

$ g++ -c 832794.c
In file included from /usr/include/c++/4.2/backward/iostream.h:31,
                 from 832794.c:1:
/usr/include/c++/4.2/backward/backward_warning.h:32:2: warning: #warni
+ng This file includes at least one deprecated or antiquated header. P
+lease consider using one of the 32 headers found in section 17.4.1.2 
+of the C++ standard. Examples include substituting the <X> header for
+ the <X.h> header for C++ includes, or <iostream> instead of the depr
+ecated header <iostream.h>. To disable this warning use -Wno-deprecat
+ed.

$ gcc -c 832794.c
832794.c:1:22: error: iostream.h: No such file or directory
[download]

...which is exactly the first error the OP is getting:

_01basic_t_5cd2.xs:2:22: iostream.h: No such file or directory
[download]

(Just to be clear: the primary issue here is not the deprecation warning, but the fact that the path were iostream.h resides isn't being searched when gcc is used.  The warning is just an indication that Inline::CPP is rather old/unmaintained.)