Ask brew for valgrind include path

Valgrind is typically installed using brew on macOS. This commit
makes ./configure detect this case set the appropriate include
directory (in the same way as we already do for openssl and gmp).

build-aux/m4/bitcoin_secp.m4

@@ -87,3 +87,11 @@ if test x"$has_gmp" != x"yes"; then
   LIBS="$LIBS_TEMP"
 fi
 ])
+
+AC_DEFUN([SECP_VALGRIND_CHECK],[
+if test x"$has_valgrind" != x"yes"; then
+  CPPFLAGS_TEMP="$CPPFLAGS"
+  CPPFLAGS="$VALGRIND_CPPFLAGS $CPPFLAGS"
+  AC_CHECK_HEADER([valgrind/memcheck.h], [has_valgrind=yes; AC_DEFINE(HAVE_VALGRIND,1,[Define this symbol if valgrind is installed])])
+fi
+])

configure.ac

@@ -40,9 +40,9 @@ case $host_os in
          dnl These Homebrew packages may be keg-only, meaning that they won't be found
          dnl in expected paths because they may conflict with system files. Ask
          dnl Homebrew where each one is located, then adjust paths accordingly.
-
          openssl_prefix=`$BREW --prefix openssl 2>/dev/null`
          gmp_prefix=`$BREW --prefix gmp 2>/dev/null`
+         valgrind_prefix=`$BREW --prefix valgrind 2>/dev/null`
          if test x$openssl_prefix != x; then
            PKG_CONFIG_PATH="$openssl_prefix/lib/pkgconfig:$PKG_CONFIG_PATH"
            export PKG_CONFIG_PATH
@@ -52,6 +52,9 @@ case $host_os in
            GMP_CPPFLAGS="-I$gmp_prefix/include"
            GMP_LIBS="-L$gmp_prefix/lib"
          fi
+         if test x$valgrind_prefix != x; then
+           VALGRIND_CPPFLAGS="-I$valgrind_prefix/include"
+         fi
        else
          AC_PATH_PROG([PORT],port,)
          dnl if homebrew isn't installed and macports is, add the macports default paths
@@ -180,12 +183,15 @@ AC_ARG_WITH([valgrind], [AS_HELP_STRING([--with-valgrind=yes|no|auto],
 if test x"$req_valgrind" = x"no"; then
   enable_valgrind=no
 else
-  AC_CHECK_HEADER([valgrind/memcheck.h], [enable_valgrind=yes], [
+  SECP_VALGRIND_CHECK
+  if test x"$has_valgrind" != x"yes"; then
     if test x"$req_valgrind" = x"yes"; then
       AC_MSG_ERROR([Valgrind support explicitly requested but valgrind/memcheck.h header not available])
     fi
     enable_valgrind=no
-  ], [])
+  else
+    enable_valgrind=yes
+  fi
 fi
 AM_CONDITIONAL([VALGRIND_ENABLED],[test "$enable_valgrind" = "yes"])
 
@@ -424,6 +430,10 @@ if test x"$set_bignum" = x"gmp"; then
   SECP_INCLUDES="$SECP_INCLUDES $GMP_CPPFLAGS"
 fi
 
+if test x"$enable_valgrind" = x"yes"; then
+  SECP_INCLUDES="$SECP_INCLUDES $VALGRIND_CPPFLAGS"
+fi
+
 if test x"$set_precomp" = x"yes"; then
   AC_DEFINE(USE_ECMULT_STATIC_PRECOMPUTATION, 1, [Define this symbol to use a statically generated ecmult table])
 fi