bug#31981: 26.1; flymake: removes temporary file before finishing check

[Enrico Scholz <enrico.scholz@sigma-chemnitz.de>]

flymake gets confused and terminates itself when checking needs a long
time.  It can be reproduced with a makefile like

--- Makefile ---
check-syntax:
	sleep 2
	${MAKE} ${CHK_SOURCES}
----------------

1. start 'emacs -Q'

2. open 'foo.c' in the directory with the makefile above

3. M-x flymake-mode

4. start typing

   --> "Wait" appears in status line

5. continue typing

   --> "!" appears in status line and log reports


  | Warning [flymake-proc foo.c]: deleted file /tmp/YYY/foo_flymake.c
  | Warning [flymake-proc  *flymake output for foo.c*-919402]: Reference to file e: *** [Makefile is out of scope
  | Warning [flymake-proc  *flymake output for foo.c*-131024]: Reference to file e: *** [Makefile is out of scope
  | Warning [flymake-proc foo.c]: process 2803326 exited with code 2
  | Error [flymake-proc foo.c]: :configuration-error: Command (make -s -C ./ CHK_SOURCES=foo_flymake.c SYNTAX_CHECK_MODE=1 check-syntax) errored, but no diagnostics
  | Warning [flymake foo.c]: Disabling backend flymake-proc-legacy-flymake because :configuration-error: Command (make -s -C ./ CHK_SOURCES=foo_flymake.c SYNTAX_CHECK_MODE=1 check-syntax) errored, but no diagnostics




--------------
GNU Emacs 26.1 (build 1, x86_64-redhat-linux-gnu, GTK+ Version 2.24.32)
 of 2018-05-31 built on koji-builder4.intern.sigma-chemnitz.de
Windowing system distributor 'Fedora Project', version 11.0.11906000
System Description:	Fedora release 28 (Twenty Eight)

...

Configured using:
 'configure --build=x86_64-redhat-linux-gnu
 --host=x86_64-redhat-linux-gnu --program-prefix=
 --disable-dependency-tracking --prefix=/usr --exec-prefix=/usr
 --bindir=/usr/bin --sbindir=/usr/sbin --sysconfdir=/etc
 --datadir=/usr/share --includedir=/usr/include --libdir=/usr/lib64
 --libexecdir=/usr/libexec --localstatedir=/var
 --sharedstatedir=/var/lib --mandir=/usr/share/man
 --infodir=/usr/share/info --with-dbus --with-gif --with-jpeg --with-png
 --with-rsvg --with-tiff --with-xft --with-xpm --with-x-toolkit=gtk
 --with-gpm=no --with-modules build_alias=x86_64-redhat-linux-gnu
 host_alias=x86_64-redhat-linux-gnu 'CFLAGS=-DMAIL_USE_LOCKF -O2 -g
 -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2
 -Wp,-D_GLIBCXX_ASSERTIONS -fexceptions -fstack-protector-strong
 -grecord-gcc-switches -specs=/usr/lib/rpm/redhat/redhat-hardened-cc1
 -specs=/usr/lib/rpm/redhat/redhat-annobin-cc1 -m64 -mtune=generic
 -fasynchronous-unwind-tables -fstack-clash-protection -fcf-protection'
 LDFLAGS=-Wl,-z,relro
 PKG_CONFIG_PATH=:/usr/lib64/pkgconfig:/usr/share/pkgconfig'

Configured features:
XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND DBUS GSETTINGS NOTIFY ACL
LIBSELINUX GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB
TOOLKIT_SCROLL_BARS GTK2 X11 MODULES THREADS LCMS2

Important settings:
  value of $LC_COLLATE: C
  value of $LANG: de_DE.UTF-8
  locale-coding-system: utf-8-unix