Remove ${srcroot} from cfghdrs_in, cfgoutputs_in and cfghdrs_tup in configure
On Windows, srcroot may start with "drive:", which confuses autoconf's
AC_CONFIG_* macros. The macros works equally well without ${srcroot},
provided some adjustment to Makefile.in.
diff --git a/Makefile.in b/Makefile.in
index 839bb08..a21acd4 100644
--- a/Makefile.in
+++ b/Makefile.in
@@ -42,9 +42,9 @@
AUTOCONF := @AUTOCONF@
_RPATH = @RPATH@
RPATH = $(if $(1),$(call _RPATH,$(1)))
-cfghdrs_in := @cfghdrs_in@
+cfghdrs_in := $(addprefix $(srcroot),@cfghdrs_in@)
cfghdrs_out := @cfghdrs_out@
-cfgoutputs_in := @cfgoutputs_in@
+cfgoutputs_in := $(addprefix $(srcroot),@cfgoutputs_in@)
cfgoutputs_out := @cfgoutputs_out@
enable_autogen := @enable_autogen@
enable_code_coverage := @enable_code_coverage@