fix building on Cygwin

Cygwin still doesn't support any of the backtrace functions. Also, remove a
spurious newline from a debug message.

Fixes #2993

configure.ac

@@ -217,7 +217,6 @@ CXXFLAGS="$CXXFLAGS -Wall -Wno-sign-compare"
 #
 # This is needed in order to get the really cool backtraces on Linux
 #
-
 AC_MSG_CHECKING([for -rdynamic linker flag])
 prev_LDFLAGS="$LDFLAGS"
 LDFLAGS="$LDFLAGS -rdynamic"
@@ -268,7 +267,6 @@ AC_SEARCH_LIBS( shm_open, rt, , [AC_MSG_ERROR([Cannot find the rt library, neede
 AC_SEARCH_LIBS( pthread_create, pthread, , [AC_MSG_ERROR([Cannot find the pthread library, needed to build this package.] )] )
 AC_SEARCH_LIBS( setupterm, [ncurses tinfo curses], , [AC_MSG_ERROR([Could not find a curses implementation, needed to build fish. If this is Linux, try running 'sudo apt-get install libncurses5-dev' or 'sudo yum install ncurses-devel'])] )
 AC_SEARCH_LIBS( [nan], [m], [AC_DEFINE( [HAVE_NAN], [1], [Define to 1 if you have the nan function])] )
-AC_SEARCH_LIBS( [backtrace_symbols_fd], [execinfo] )
 AC_SEARCH_LIBS( [dladdr], [dl] )
 
 if test x$local_gettext != xno; then
@@ -313,7 +311,7 @@ AC_STRUCT_DIRENT_D_TYPE
 AC_CHECK_FUNCS( wcsndup )
 AC_CHECK_FUNCS( futimes )
 AC_CHECK_FUNCS( wcslcat wcslcpy lrand48_r killpg )
-AC_CHECK_FUNCS( backtrace backtrace_symbols_fd getifaddrs )
+AC_CHECK_FUNCS( backtrace_symbols getifaddrs )
 AC_CHECK_FUNCS( futimens clock_gettime )
 
 AC_CHECK_DECL( [mkostemp], [ AC_CHECK_FUNCS([mkostemp]) ] )

src/common.cpp

@@ -70,7 +70,9 @@ static volatile bool termsize_valid;
 static rwlock_t termsize_rwlock;
 
 static char *wcs2str_internal(const wchar_t *in, char *out);
+static void debug_shared(const wchar_t msg_level, const wcstring &msg);
 
+#ifdef HAVE_BACKTRACE_SYMBOLS
 // This function produces a stack backtrace with demangled function & method names. It is based on
 // https://gist.github.com/fmela/591333 but adapted to the style of the fish project.
 static const wcstring_list_t __attribute__((noinline))
@@ -104,7 +106,6 @@ demangled_backtrace(int max_frames, int skip_levels) {
     return backtrace_text;
 }
 
-static void debug_shared(const wchar_t msg_level, const wcstring &msg);
 void __attribute__((noinline)) show_stackframe(const wchar_t msg_level, int frame_count,
                                                int skip_levels) {
     ASSERT_IS_NOT_FORKED_CHILD();
@@ -124,6 +125,14 @@ void __attribute__((noinline)) show_stackframe(const wchar_t msg_level, int fram
     }
 }
 
+#else // HAVE_BACKTRACE_SYMBOLS
+
+void __attribute__((noinline)) show_stackframe(const wchar_t msg_level, int frame_count,
+                                               int skip_levels) {
+    debug_shared(msg_level, L"Sorry, but your system does not support backtraces");
+}
+#endif // HAVE_BACKTRACE_SYMBOLS
+
 int fgetws2(wcstring *s, FILE *f) {
     int i = 0;
     wint_t c;

src/exec.cpp

@@ -1058,7 +1058,7 @@ void exec_job(parser_t &parser, job_t *j) {
 
                     // A 0 pid means we failed to posix_spawn. Since we have no pid, we'll never get
                     // told when it's exited, so we have to mark the process as failed.
-                    debug(2, L"Fork #%d, pid %d: spawn external command '%s' from '%ls'\n",
+                    debug(2, L"Fork #%d, pid %d: spawn external command '%s' from '%ls'",
                           g_fork_count, pid, actual_cmd, file ? file : L"<no file>");
                     if (pid == 0) {
                         job_mark_process_as_failed(j, p);

src/fallback.cpp

@@ -332,14 +332,6 @@ int killpg(int pgr, int sig) {
 }
 #endif
 
-#ifndef HAVE_BACKTRACE
-int backtrace(void **buffer, int size) { return 0; }
-#endif
-
-#ifndef HAVE_BACKTRACE_SYMBOLS_FD
-char **backtrace_symbols_fd(void *const *buffer, int size, int fd) { return 0; }
-#endif
-
 #ifndef HAVE_NAN
 double nan(char *tagp) { return 0.0 / 0.0; }
 #endif

src/fallback.h

@@ -149,12 +149,4 @@ int killpg(int pgr, int sig);
 double nan(char *tagp);
 #endif
 
-#ifndef HAVE_BACKTRACE
-int backtrace(void **buffer, int size);
-#endif
-
-#ifndef HAVE_BACKTRACE_SYMBOLS_FD
-char **backtrace_symbols_fd(void *const *buffer, int size, int fd);
-#endif
-
 #endif