guile: Change return value of gdbscm_with_guile for const char *

The documentation of gdbscm_with_guile says that it returns a statically
allocated string (IOW, a const char *).  We can reflect that in its
return value type, and get rid of C++ build errors.

Initially fixes:

/home/simark/src/binutils-gdb/gdb/guile/scm-disasm.c: In function ‘void* gdbscm_disasm_read_memory_worker(void*)’:
/home/simark/src/binutils-gdb/gdb/guile/scm-disasm.c:93:12: error: invalid conversion from ‘const void*’ to ‘void*’ [-fpermissive]
     return "seek error";

gdb/ChangeLog:

	* guile/guile-internal.h (gdbscm_with_guile): Change return
	types to const char *.
	* guile/scm-safe-call.c (gdbscm_with_guile): Likewise.
	(struct c_data) <func>: Likewise.
	(struct c_data) <result>: Change type to const char *.
	(scscm_eval_scheme_string): Change return type to
	const char *.
	(scscm_source_scheme_script): Likewise.
	(gdbscm_safe_eval_string): Change type of result variable to
	const char * and remove cast.
	(gdbscm_safe_source_script): Likewise.
	* guile/scm-disasm.c (gdbscm_disasm_read_memory_worker):
	Change return type to const char *.
	(gdbscm_disasm_read_memory): Change type of status to
	const char *.

1 files changed, 2 insertions, 2 deletions

diff --git a/gdb/guile/scm-disasm.c b/gdb/guile/scm-disasm.c
index d1572c7..78b38df 100644
--- a/gdb/guile/scm-disasm.c
+++ b/gdb/guile/scm-disasm.c
@@ -76,7 +76,7 @@ dascm_make_insn (CORE_ADDR pc, const char *assembly, int insn_len)
    Scheme port.  Called via gdbscm_call_guile.
    The result is a statically allocated error message or NULL if success.  */
 
-static void *
+static const char *
 gdbscm_disasm_read_memory_worker (void *datap)
 {
   struct gdbscm_disasm_read_data *data
@@ -109,7 +109,7 @@ gdbscm_disasm_read_memory (bfd_vma memaddr, bfd_byte *myaddr,
 			   struct disassemble_info *dinfo)
 {
   struct gdbscm_disasm_read_data data;
-  void *status;
+  const char *status;
 
   data.memaddr = memaddr;
   data.myaddr = myaddr;