ash: support platforms that don't have '%m' printf specifier

The '%m' conversion specifier prints an error message based on the
current value of 'errno'.  It is available in the GNU C library,
Cygwin (since 2012), uClibc and musl.

It is not available in various BSDs, BSD-derived systems (MacOS,
Android) or Microsoft Windows.

Use a symbol defined in platform.h to control how error messages
can be formatted to display the 'errno' message.  On platforms that
support it use '%m'; on other platforms use '%s' and strerror().

On platforms that have '%m' there is essentially no change in the
size of the binary.  Otherwise:

function                                             old     new   delta
redirect                                            1287    1310     +23
xtcsetpgrp                                            27      44     +17
dup2_or_raise                                         34      51     +17
setinputfile                                         267     275      +8
.rodata                                           163379  163371      -8
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 4/1 up/down: 65/-8)              Total: 57 bytes

Signed-off-by: Ron Yorston <rmy@pobox.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/include/platform.h b/include/platform.h
index ea49c7e92..b81c59d4e 100644
--- a/include/platform.h
+++ b/include/platform.h
@@ -406,6 +406,7 @@ typedef unsigned smalluint;
 #define HAVE_MNTENT_H 1
 #define HAVE_NET_ETHERNET_H 1
 #define HAVE_SYS_STATFS_H 1
+#define HAVE_PRINTF_PERCENTM 1
 
 #if defined(__UCLIBC__)
 # if UCLIBC_VERSION < KERNEL_VERSION(0, 9, 32)
@@ -461,6 +462,7 @@ typedef unsigned smalluint;
 # undef HAVE_DPRINTF
 # undef HAVE_UNLOCKED_STDIO
 # undef HAVE_UNLOCKED_LINE_OPS
+# undef HAVE_PRINTF_PERCENTM
 #endif
 
 #if defined(__dietlibc__)
@@ -483,6 +485,7 @@ typedef unsigned smalluint;
 # undef HAVE_STRVERSCMP
 # undef HAVE_XTABS
 # undef HAVE_UNLOCKED_LINE_OPS
+# undef HAVE_PRINTF_PERCENTM
 # include <osreldate.h>
 # if __FreeBSD_version < 1000029
 #  undef HAVE_STRCHRNUL /* FreeBSD added strchrnul() between 1000028 and 1000029 */
@@ -517,6 +520,7 @@ typedef unsigned smalluint;
 # undef HAVE_STRVERSCMP
 # undef HAVE_UNLOCKED_LINE_OPS
 # undef HAVE_NET_ETHERNET_H
+# undef HAVE_PRINTF_PERCENTM
 #endif
 
 /*