Merge bitcoin#24048: build: Improve error message when pkg-config is not installed

18f304d build: Improve error message when pkg-config is not installed (Hennadii Stepanov)

Pull request description:

  Fixes bitcoin#24037.

  With this PR:
  ```
  # ./autogen.sh
  configure.ac:16: error: PKG_PROG_PKG_CONFIG macro not found. Please install pkg-config and re-run autogen.sh
  configure.ac:16: the top level
  autom4te: /usr/bin/m4 failed with exit status: 1
  aclocal: error: /usr/bin/autom4te failed with exit status: 1
  autoreconf: aclocal failed with exit status: 1
  ```

ACKs for top commit:
  laanwj:
    Tested ACK 18f304d
  jarolrod:
    ACK 18f304d

Tree-SHA512: ba845f44c966fea6cf7cee0db9cacc431072e2005ad065c8f2bbe3cffd8415c3af6ed443cccf9606df7de4df2ff3e72636afb5f3776d2a96af8572aab7018549

Author: laanwj

configure.ac

@@ -13,7 +13,7 @@ AC_CONFIG_HEADERS([src/config/bitcoin-config.h])
 AC_CONFIG_AUX_DIR([build-aux])
 AC_CONFIG_MACRO_DIR([build-aux/m4])
 
-m4_ifndef([PKG_PROG_PKG_CONFIG], [AC_MSG_ERROR([PKG_PROG_PKG_CONFIG macro not found. Please install pkg-config and re-run autogen.sh])])
+m4_ifndef([PKG_PROG_PKG_CONFIG], [m4_fatal([PKG_PROG_PKG_CONFIG macro not found. Please install pkg-config and re-run autogen.sh])])
 PKG_PROG_PKG_CONFIG
 if test "$PKG_CONFIG" = ""; then
   AC_MSG_ERROR([pkg-config not found])