Merge bitcoin#891: build: Add workaround for automake 1.13 and older

f329bba build: Add workaround for automake 1.13 and older (Tim Ruffing)

Pull request description:

  Fixes bitcoin#890.

ACKs for top commit:
  michaelfolkson:
    ACK f329bba

Tree-SHA512: 1ae3d1587abb402c2d3bb28d3a48aeff056f061e755d65d482204bb502b8427aad376c7319b4a694a5bf79c193acd3c88cb65928f0bc0e5c7587222e1315b6d0

configure.ac

@@ -23,7 +23,15 @@ AC_PATH_TOOL(AR, ar)
 AC_PATH_TOOL(RANLIB, ranlib)
 AC_PATH_TOOL(STRIP, strip)
 
+# Save definition of AC_PROG_CC because AM_PROG_CC_C_O in automake<=1.13 will
+# redefine AC_PROG_CC to exit with an error, which avoids the user calling it
+# accidently and screwing up the effect of AM_PROG_CC_C_O. However, we'll need
+# AC_PROG_CC later on in AX_PROG_CC_FOR_BUILD, where its usage is fine, and
+# we'll carefully make sure not to call AC_PROG_CC anywhere else.
+m4_copy([AC_PROG_CC], [saved_AC_PROG_CC])
 AM_PROG_CC_C_O
+# Restore AC_PROG_CC
+m4_rename_force([saved_AC_PROG_CC], [AC_PROG_CC])
 
 AC_PROG_CC_C89
 if test x"$ac_cv_prog_cc_c89" = x"no"; then