Merge bitcoin#813: Enable configuring Valgrind support

412bf87 configure: Allow specifying --with[out]-valgrind explicitly (Luke Dashjr)

Pull request description:

ACKs for top commit:
  sipa:
    ACK 412bf87. Tested by running configure on a system with and without valgrind, and with no argument, with `--with-valgrind`, and with `--without-valgrind`.
  real-or-random:
    ACK 412bf87
  jonasnick:
    ACK 412bf87

Tree-SHA512: 92417609751e5af813faff1661055cd37f3d00dbcf109a8f14f8ba59d9f3d620c9c6b67d2b1629b6ab75e2afcd47d2b3898a0427931567fb505bc92fa5ee3532

configure.ac

@@ -178,7 +178,21 @@ AC_ARG_WITH([ecmult-gen-precision], [AS_HELP_STRING([--with-ecmult-gen-precision
 )],
 [req_ecmult_gen_precision=$withval], [req_ecmult_gen_precision=auto])
 
-AC_CHECK_HEADER([valgrind/memcheck.h], [enable_valgrind=yes], [enable_valgrind=no], [])
+AC_ARG_WITH([valgrind], [AS_HELP_STRING([--with-valgrind=yes|no|auto],
+[Build with extra checks for running inside Valgrind [default=auto]]
+)],
+[req_valgrind=$withval], [req_valgrind=auto])
+
+if test x"$req_valgrind" = x"no"; then
+  enable_valgrind=no
+else
+  AC_CHECK_HEADER([valgrind/memcheck.h], [enable_valgrind=yes], [
+    if test x"$req_valgrind" = x"yes"; then
+      AC_MSG_ERROR([Valgrind support explicitly requested but valgrind/memcheck.h header not available])
+    fi
+    enable_valgrind=no
+  ], [])
+fi
 AM_CONDITIONAL([VALGRIND_ENABLED],[test "$enable_valgrind" = "yes"])
 
 if test x"$enable_coverage" = x"yes"; then