Fix build on systems where libc relies on <linux/signal.h>

Commit v4.23~10 has broken the build with Android's libc because it
relies on the UAPI headers (such as <linux/signal.h>) to define various
types, rather than copying them into the libc headers (such as <signal.h>)
like most other Linux C libraries.

* linux/linux/signal.h: Rename to linux/signal.h.in.
* Makefile.am (strace_SOURCES): Remove linux/linux/signal.h.
(EXTRA_DIST): Add linux/signal.h.in.
(DISTCLEANFILES): Add linux/linux/signal.h.
* configure.ac (AC_CACHE_CHECK): Check whether <linux/signal.h>
can be used along with <signal.h>, install linux/linux/signal.h
workaround if they cannot be used together.

Reported-by: Elliott Hughes <enh@google.com>
Closes: https://github.com/strace/strace/issues/72

Makefile.am

@@ -182,7 +182,6 @@ strace_SOURCES =	\
 	ldt.c		\
 	link.c		\
 	linux/asm_stat.h \
-	linux/linux/signal.h \
 	linux/x32/asm_stat.h \
 	linux/x86_64/asm_stat.h \
 	listen.c	\
@@ -804,6 +803,7 @@ EXTRA_DIST =				\
 	linux/sh64/syscallent.h		\
 	linux/sh64/userent.h		\
 	linux/shuffle_scno.c		\
+	linux/signal.h.in 		\
 	linux/signalent.h		\
 	linux/smc_diag.h		\
 	linux/sock_diag.h		\
@@ -1042,7 +1042,7 @@ CLEANFILES    = $(ioctl_redefs_h) $(ioctlent_h) $(mpers_preproc_files) \
 		ioctl_iocdef.h ioctl_iocdef.i \
 		bpf_attr_check.c native_printer_decls.h native_printer_defs.h \
 		printers.h sen.h sys_func.h
-DISTCLEANFILES = gnu/stubs-32.h gnu/stubs-x32.h
+DISTCLEANFILES = gnu/stubs-32.h gnu/stubs-x32.h linux/linux/signal.h
 
 include scno.am
 

configure.ac

@@ -581,8 +581,22 @@ AC_CHECK_TYPES(m4_normalize([
 ]),,, [#include <linux/kvm.h>])
 
 saved_CPPFLAGS="$CPPFLAGS"
-CPPFLAGS="$CPPFLAGS -I$srcdir/linux"
+
+AC_CACHE_CHECK([whether <linux/signal.h> can be used along with <signal.h>],
+	       [st_cv_linux_signal],
+	       [AC_COMPILE_IFELSE([AC_LANG_SOURCE([[
+#include <signal.h>
+#include <linux/signal.h>]],[])],
+				  [st_cv_linux_signal=yes],
+				  [st_cv_linux_signal=no])])
+if test "x$st_cv_linux_signal" = xno; then
+	mkdir -p linux/linux
+	cp $srcdir/linux/signal.h.in linux/linux/signal.h
+	CPPFLAGS="$CPPFLAGS -Ilinux"
+fi
+
 AC_CHECK_TYPES([struct __aio_sigset],,, [#include <linux/aio_abi.h>])
+
 CPPFLAGS="$saved_CPPFLAGS"
 
 AC_CHECK_HEADERS([linux/btrfs.h], [