In MinGW build, avoid clash between libguile and SRFI library function names

The dummy scm_init_* and scm_c_init_* functions in the empty libraries
for SRFIs 4, 13 and 14 clash with declarations with the same names in
libguile.h that are marked (in the MinGW build) with __declspec
(dllimport).  These libraries are empty because their content was
moved into libguile some time ago, and I think these functions are
needed only so that the libraries appear to contain something.  They
used also to be needed for the (load-extension ...)  forms in the
corresponding .scm modules, but those forms were not needed anymore,
and so were removed, when everything moved into libguile.

* srfi/srfi-13.c (scm_init_srfi_13_no_clash_with_libguile): Renamed
  from scm_init_srfi_13.
  (scm_init_srfi_13_14_no_clash_with_libguile): Same.

* srfi/srfi-14.c (scm_init_srfi_14_no_clash_with_libguile): Same.
  (scm_c_init_srfi_14_no_clash_with_libguile): Same.

* srfi/srfi-4.c (scm_init_srfi_4_no_clash_with_libguile): Same.

srfi/srfi-13.c

@@ -29,12 +29,15 @@
 
 #include <srfi/srfi-13.h>
 
+void scm_init_srfi_13_no_clash_with_libguile (void);
+void scm_init_srfi_13_14_no_clash_with_libguile (void);
+
 void
-scm_init_srfi_13 (void)
+scm_init_srfi_13_no_clash_with_libguile (void)
 {
 }
 
 void
-scm_init_srfi_13_14 (void)
+scm_init_srfi_13_14_no_clash_with_libguile (void)
 {
 }

srfi/srfi-14.c

@@ -23,12 +23,15 @@
 
 #include <srfi/srfi-14.h>
 
+void scm_init_srfi_14_no_clash_with_libguile (void);
+void scm_c_init_srfi_14_no_clash_with_libguile (void);
+
 void
-scm_init_srfi_14 (void)
+scm_init_srfi_14_no_clash_with_libguile (void)
 {
 }
 
 void
-scm_c_init_srfi_14 (void)
+scm_c_init_srfi_14_no_clash_with_libguile (void)
 {
 }

srfi/srfi-4.c

@@ -28,8 +28,10 @@
 
 #include <srfi/srfi-4.h>
 
+void scm_init_srfi_4_no_clash_with_libguile (void);
+
 void
-scm_init_srfi_4 (void)
+scm_init_srfi_4_no_clash_with_libguile (void)
 {
 }