Merge #19356: build: Fix search for brew-installed BDB 4 on OS X

8578c6fccd build: Fix search for brew-installed BDB 4 on OS X (Glenn Willen)

Pull request description:

  ~~NOTE: This PR contains one important fix that I need (to make Bitcoin Core build cleanly on my system without shenanigans), plus some related general cleanup that is not really necessary, and could be annoying. (I am prepared to defend my argument that BDB_CFLAGS is wrong here, and BDB_CPPFLAGS is right, but this could bite anybody who has gotten in the habit of -- or scripted -- setting the former.)~~

  Ok, I have been convinced that I was too clever with the refactor and I have removed it. Now it's just the tiny change to fix the build on my local machine.

  ---

  On OS X, when searching Homebrew keg-only packages for BDB 4.8, if we find it,
  use BDB_CPPFLAGS and BDB_LIBS instead of CFLAGS and LIBS for the result. This
  is (1) more correct, and (2) necessary in order to give this location
  priority over other directories in the include search path, which may include
  system include directories with other versions of BDB.

ACKs for top commit:
  theuni:
    ACK 8578c6fccd.

Tree-SHA512: a28f48fc81a25736f7e77c663f21cd9a6ae1cd115682031c5aa695c94cb5afa11920330a60cd6a54832822a2aec1eb23123ac2e2dcd4f0b3835aef9c9339ac97

configure.ac

@@ -635,9 +635,10 @@ case $host in
 
          bdb_prefix=$($BREW --prefix berkeley-db4 2>/dev/null)
          qt5_prefix=$($BREW --prefix qt5 2>/dev/null)
-         if test x$bdb_prefix != x; then
-           CPPFLAGS="$CPPFLAGS -I$bdb_prefix/include"
-           LIBS="$LIBS -L$bdb_prefix/lib"
+         if test x$bdb_prefix != x && test "x$BDB_CFLAGS" = "x" && test "x$BDB_LIBS" = "x"; then
+           dnl This must precede the call to BITCOIN_FIND_BDB48 below.
+           BDB_CFLAGS="-I$bdb_prefix/include"
+           BDB_LIBS="-L$bdb_prefix/lib -ldb_cxx-4.8"
          fi
          if test x$qt5_prefix != x; then
            PKG_CONFIG_PATH="$qt5_prefix/lib/pkgconfig:$PKG_CONFIG_PATH"