Merge bitcoin/bitcoin#24397: build: Fix Boost.Process check for Boost 1.73 and older

774323e ci: Force `--enable-external-signer` to prevent future regressions (Hennadii Stepanov)
6997885 build: Fix Boost.Process check for Boost 1.73 and older (Hennadii Stepanov)
2199ef7 build: Fix a non-portable use of `test` (Hennadii Stepanov)
d436c48 build, refactor: Replace tabs with spaces (Hennadii Stepanov)

Pull request description:

  On master (5f44c5c) Boost.Process check false fails without the `-lpthread` flag.

  ```
  $ grep -C 2 pthread_detach config.log
  /usr/bin/ld: /tmp/cczCQfQv.o: in function `boost::asio::detail::posix_global_impl<boost::asio::system_context>::~posix_global_impl()':
  conftest.cpp:(.text._ZN5boost4asio6detail17posix_global_implINS0_14system_contextEED2Ev[_ZN5boost4asio6detail17posix_global_implINS0_14system_contextEED5Ev]+0xa3): undefined reference to `pthread_join'
  /usr/bin/ld: conftest.cpp:(.text._ZN5boost4asio6detail17posix_global_implINS0_14system_contextEED2Ev[_ZN5boost4asio6detail17posix_global_implINS0_14system_contextEED5Ev]+0xc4): undefined reference to `pthread_detach'
  collect2: error: ld returned 1 exit status
  configure:26674: $? = 1
  ```

  Not required for Boost 1.74+.

ACKs for top commit:
  laanwj:
    Code review ACK 774323e, is a bugfix/workaround, seems fine to merge last minute for 23.0.

Tree-SHA512: 2a9d4b67fd8910e107af972d8c223286b7c933bc310616f86c8b6d8c903438916980fc76bd7e37f2698f6ce5361dc706cbf2933d1ac2c081bcabe1b83ca7d6b6

Author: laanwj

ci/test/00_setup_env_win64.sh

@@ -13,4 +13,4 @@ export DPKG_ADD_ARCH="i386"
 export PACKAGES="python3 nsis g++-mingw-w64-x86-64 wine-binfmt wine64 wine32 file"
 export RUN_FUNCTIONAL_TESTS=false
 export GOAL="deploy"
-export BITCOIN_CONFIG="--enable-reduce-exports --disable-gui-tests"
+export BITCOIN_CONFIG="--enable-reduce-exports --disable-external-signer --disable-gui-tests"

ci/test/06_script_a.sh

@@ -14,7 +14,7 @@ if [ -n "$ANDROID_TOOLS_URL" ]; then
   exit 0
 fi
 
-BITCOIN_CONFIG_ALL="--enable-suppress-external-warnings --disable-dependency-tracking --prefix=$DEPENDS_DIR/$HOST --bindir=$BASE_OUTDIR/bin --libdir=$BASE_OUTDIR/lib"
+BITCOIN_CONFIG_ALL="--enable-external-signer --enable-suppress-external-warnings --disable-dependency-tracking --prefix=$DEPENDS_DIR/$HOST --bindir=$BASE_OUTDIR/bin --libdir=$BASE_OUTDIR/lib"
 if [ -z "$NO_WERROR" ]; then
   BITCOIN_CONFIG_ALL="${BITCOIN_CONFIG_ALL} --enable-werror"
 fi

configure.ac

@@ -359,7 +359,7 @@ esac
 if test "$enable_debug" = "yes"; then
   dnl Clear default -g -O2 flags
   if test "$CXXFLAGS_overridden" = "no"; then
-	CXXFLAGS=""
+  CXXFLAGS=""
   fi
 
   dnl Disable all optimizations
@@ -978,14 +978,14 @@ AC_CHECK_DECLS([setsid])
 AC_CHECK_DECLS([pipe2])
 
 AC_CHECK_DECLS([le16toh, le32toh, le64toh, htole16, htole32, htole64, be16toh, be32toh, be64toh, htobe16, htobe32, htobe64],,,
-		[#if HAVE_ENDIAN_H
+    [#if HAVE_ENDIAN_H
                  #include <endian.h>
                  #elif HAVE_SYS_ENDIAN_H
                  #include <sys/endian.h>
                  #endif])
 
 AC_CHECK_DECLS([bswap_16, bswap_32, bswap_64],,,
-		[#if HAVE_BYTESWAP_H
+    [#if HAVE_BYTESWAP_H
                  #include <byteswap.h>
                  #endif])
 
@@ -1438,11 +1438,15 @@ if test "$use_external_signer" != "no"; then
     ;;
     *)
       AC_MSG_CHECKING([whether Boost.Process can be used])
+      TEMP_LDFLAGS="$LDFLAGS"
+      dnl Boost 1.73 and older require the following workaround.
+      LDFLAGS="$LDFLAGS $PTHREAD_CFLAGS"
       AC_LINK_IFELSE([AC_LANG_PROGRAM([[#include <boost/process.hpp>]])],
         [have_boost_process="yes"],
         [have_boost_process="no"])
+      LDFLAGS="$TEMP_LDFLAGS"
       AC_MSG_RESULT([$have_boost_process])
-      if test "$have_boost_process" == "yes"; then
+      if test "$have_boost_process" = "yes"; then
         use_external_signer="yes"
         AC_DEFINE([ENABLE_EXTERNAL_SIGNER], [1], [Define if external signer support is enabled])
       else