Install BTest with Zeek

Configuring with --disable-btest skips the installation. The main
reason for doing this is that many Zeek packages come with testsuites
that nearly always require btest, so providing btest out of the box
makes sense. Note that zkg's recent additions to its PATH environment
variable management mean that this btest instance is automatically
found also when the Zeek installation's binary folder isn't in the
path.

CMakeLists.txt

@@ -568,6 +568,7 @@ add_subdirectory(man)
 
 include(CheckOptionalBuildSources)
 
+CheckOptionalBuildSources(auxil/btest BTest INSTALL_BTEST)
 CheckOptionalBuildSources(auxil/package-manager ZKG INSTALL_ZKG)
 CheckOptionalBuildSources(auxil/zeekctl   ZeekControl INSTALL_ZEEKCTL)
 CheckOptionalBuildSources(auxil/zeek-aux  Zeek-Aux  INSTALL_AUX_TOOLS)
@@ -616,6 +617,7 @@ message(
     "\n"
     "\nZeekControl:       ${INSTALL_ZEEKCTL}"
     "\nAux. Tools:        ${INSTALL_AUX_TOOLS}"
+    "\nBTest:             ${INSTALL_BTEST}"
     "\nzkg:               ${INSTALL_ZKG}"
     "\n"
     "\nlibmaxminddb:      ${USE_GEOIP}"

auxil/btest

@@ -1 +1 @@
-Subproject commit b1de8a637bc006587f5863ada6275aa76c77be7a
+Subproject commit babcafd692110d70fdc49ed28ae0bf121d662884

configure

@@ -65,6 +65,7 @@ Usage: $0 [OPTION]... [VAR=VALUE]...
     --disable-zeekctl      don't install ZeekControl
     --disable-auxtools     don't build or install auxiliary tools
     --disable-archiver     don't build or install zeek-archiver tool
+    --disable-btest        don't install BTest
     --disable-python       don't try to build python bindings for Broker
     --disable-broker-tests don't try to build Broker unit tests
     --disable-zkg          don't install zkg
@@ -162,6 +163,7 @@ append_cache_entry ENABLE_PERFTOOLS     BOOL   false
 append_cache_entry ENABLE_JEMALLOC      BOOL   false
 append_cache_entry BUILD_SHARED_LIBS    BOOL   true
 append_cache_entry INSTALL_AUX_TOOLS    BOOL   true
+append_cache_entry INSTALL_BTEST        BOOL   true
 append_cache_entry INSTALL_ZEEK_ARCHIVER BOOL  true
 append_cache_entry INSTALL_ZEEKCTL      BOOL   true
 append_cache_entry INSTALL_ZKG          BOOL   true
@@ -287,6 +289,9 @@ while [ $# -ne 0 ]; do
         --disable-archiver)
             append_cache_entry INSTALL_ZEEK_ARCHIVER    BOOL   false
             ;;
+        --disable-btest)
+            append_cache_entry INSTALL_BTEST BOOL false
+            ;;
         --disable-python)
             append_cache_entry DISABLE_PYTHON_BINDINGS     BOOL   true
             ;;