Move 'is_regular_file' from common-utils.c to filestuff.c

There is no reason for 'is_regular_file' to be in common-utils.c; it
belongs to 'filestuff.c'.  This commit moves the function definition
and its prototype to the appropriate files.

The motivation behind this move is a failure that happens on certain
cross-compilation environments when compiling the IPA library, due to
the way gnulib probes the need for a 'stat' call replacement.  Because
configure checks when cross-compiling are more limited, gnulib decides
that it needs to substitute the 'stat' calls its own 'rpl_stat';
however, the IPA library doesn't link with gnulib, which leads to an
error when compiling 'common-utils.c':

  ...
  /opt/x86-core2--musl--bleeding-edge-2018.09-1/bin/i686-buildroot-linux-musl-g++  -shared -fPIC -Wl,--soname=libinproctrace.so -Wl,--no-undefined -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64  -Os      -I. -I. -I./../common -I./../regformats -I./.. -I./../../include -I./../gnulib/import -Ibuild-gnulib-gdbserver/import -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -Wall -Wpointer-arith -Wno-unused -Wunused-value -Wunused-function -Wno-switch -Wno-char-subscripts -Wempty-body -Wunused-but-set-parameter -Wunused-but-set-variable -Wno-sign-compare -Wno-narrowing -Wno-error=maybe-uninitialized  -DGDBSERVER \
   -Wl,--dynamic-list=./proc-service.list -o libinproctrace.so ax-ipa.o common-utils-ipa.o errors-ipa.o format-ipa.o print-utils-ipa.o regcache-ipa.o remote-utils-ipa.o rsp-low-ipa.o tdesc-ipa.o tracepoint-ipa.o utils-ipa.o vec-ipa.o linux-i386-ipa.o linux-x86-tdesc-ipa.o arch/i386-ipa.o -ldl -pthread
  /opt/x86-core2--musl--bleeding-edge-2018.09-1/lib/gcc/i686-buildroot-linux-musl/8.2.0/../../../../i686-buildroot-linux-musl/bin/ld: common-utils-ipa.o: in function `is_regular_file(char const*, int*)':
  common-utils.c:(.text+0x695): undefined reference to `rpl_stat'
  collect2: error: ld returned 1 exit status
  Makefile:413: recipe for target 'libinproctrace.so' failed
  make[1]: *** [libinproctrace.so] Error 1
  ...

More details can also be found at:

  https://sourceware.org/ml/gdb-patches/2018-09/msg00304.html

The most simple fix for this problem is to move 'is_regular_file' to
'filestuff.c', which is not used by IPA.  This ends up making the
files more logically organized as well, since 'is_regular_file' is a
file operation.

No regressions found.

gdb/ChangeLog:
2018-09-12  Sergio Durigan Junior  <sergiodj@redhat.com>

	* common/common-utils.c: Don't include '<sys/stat.h>'.
	(is_regular_file): Move to...
	* common/filestuff.c (is_regular_file): ... here.
	* common/common-utils.h (is_regular_file): Move to...
	* common/filestuff.h (is_regular_file): ... here.

gdb/ChangeLog

@@ -1,3 +1,11 @@
+2018-09-12  Sergio Durigan Junior  <sergiodj@redhat.com>
+
+	* common/common-utils.c: Don't include '<sys/stat.h>'.
+	(is_regular_file): Move to...
+	* common/filestuff.c (is_regular_file): ... here.
+	* common/common-utils.h (is_regular_file): Move to...
+	* common/filestuff.h (is_regular_file): ... here.
+
 2018-09-12  Simon Marchi  <simon.marchi@ericsson.com>
 
 	* skip.c (debug_skip): New variable.

gdb/common/common-utils.c

@@ -20,7 +20,6 @@
 #include "common-defs.h"
 #include "common-utils.h"
 #include "host-defs.h"
-#include <sys/stat.h>
 #include <ctype.h>
 
 /* The xmalloc() (libiberty.h) family of memory management routines.
@@ -412,37 +411,6 @@ stringify_argv (const std::vector<char *> &args)
 
 /* See common/common-utils.h.  */
 
-bool
-is_regular_file (const char *name, int *errno_ptr)
-{
-  struct stat st;
-  const int status = stat (name, &st);
-
-  /* Stat should never fail except when the file does not exist.
-     If stat fails, analyze the source of error and return true
-     unless the file does not exist, to avoid returning false results
-     on obscure systems where stat does not work as expected.  */
-
-  if (status != 0)
-    {
-      if (errno != ENOENT)
-	return true;
-      *errno_ptr = ENOENT;
-      return false;
-    }
-
-  if (S_ISREG (st.st_mode))
-    return true;
-
-  if (S_ISDIR (st.st_mode))
-    *errno_ptr = EISDIR;
-  else
-    *errno_ptr = EINVAL;
-  return false;
-}
-
-/* See common/common-utils.h.  */
-
 ULONGEST
 align_up (ULONGEST v, int n)
 {

gdb/common/common-utils.h

@@ -146,11 +146,6 @@ in_inclusive_range (T value, T low, T high)
   return value >= low && value <= high;
 }
 
-/* Return true if the file NAME exists and is a regular file.
-   If the result is false then *ERRNO_PTR is set to a useful value assuming
-   we're expecting a regular file.  */
-extern bool is_regular_file (const char *name, int *errno_ptr);
-
 /* Ensure that V is aligned to an N byte boundary (B's assumed to be a
    power of 2).  Round up/down when necessary.  Examples of correct
    use include:

gdb/common/filestuff.c

@@ -417,3 +417,34 @@ make_cleanup_close (int fd)
   *saved_fd = fd;
   return make_cleanup_dtor (do_close_cleanup, saved_fd, xfree);
 }
+
+/* See common/filestuff.h.  */
+
+bool
+is_regular_file (const char *name, int *errno_ptr)
+{
+  struct stat st;
+  const int status = stat (name, &st);
+
+  /* Stat should never fail except when the file does not exist.
+     If stat fails, analyze the source of error and return true
+     unless the file does not exist, to avoid returning false results
+     on obscure systems where stat does not work as expected.  */
+
+  if (status != 0)
+    {
+      if (errno != ENOENT)
+	return true;
+      *errno_ptr = ENOENT;
+      return false;
+    }
+
+  if (S_ISREG (st.st_mode))
+    return true;
+
+  if (S_ISDIR (st.st_mode))
+    *errno_ptr = EISDIR;
+  else
+    *errno_ptr = EINVAL;
+  return false;
+}

gdb/common/filestuff.h

@@ -117,4 +117,9 @@ struct gdb_dir_deleter
 
 typedef std::unique_ptr<DIR, gdb_dir_deleter> gdb_dir_up;
 
+/* Return true if the file NAME exists and is a regular file.
+   If the result is false then *ERRNO_PTR is set to a useful value assuming
+   we're expecting a regular file.  */
+extern bool is_regular_file (const char *name, int *errno_ptr);
+
 #endif /* FILESTUFF_H */