Convert systemtap from bool to feature option type

Now systemtap can be enabled by default in distros that use
-Dauto_features=enabled or for developers who already have systemtap
installed, while it's still disabled for developers who do not have
systemtap installed. See #3354

.gitlab-ci.yml

@@ -185,7 +185,7 @@ fedora-x86_64:
             --prefix=$HOME/glib-installed
             --localstatedir=/var
             --libdir=lib
-            -Dsystemtap=true
+            -Dsystemtap=enabled
             -Ddtrace=enabled
             -Dinstalled_tests=true
             -Ddocumentation=true
@@ -240,7 +240,7 @@ debian-stable-x86_64:
             --prefix=$HOME/glib-installed
             --localstatedir=/var
             --libdir=lib
-            -Dsystemtap=true
+            -Dsystemtap=enabled
             -Ddtrace=enabled
             _build
     - meson compile -C _build
@@ -312,7 +312,7 @@ muslc-alpine-x86_64:
             --prefix=$HOME/glib-installed
             --localstatedir=/var
             --libdir=lib
-            -Dsystemtap=true
+            -Dsystemtap=enabled
             _build
     - meson compile -C _build
     - .gitlab-ci/run-tests.sh
@@ -383,7 +383,7 @@ G_DISABLE_ASSERT:
   script:
     - meson setup ${MESON_COMMON_OPTIONS}
             --werror
-            -Dsystemtap=true
+            -Dsystemtap=enabled
             -Ddtrace=enabled
             -Dinstalled_tests=true
             -Dglib_assert=false
@@ -421,7 +421,7 @@ valgrind:
   script:
     - meson setup ${MESON_COMMON_OPTIONS}
             --werror
-            -Dsystemtap=true
+            -Dsystemtap=enabled
             -Ddtrace=enabled
             -Dinstalled_tests=true
             -Dintrospection=enabled
@@ -766,7 +766,7 @@ scan-build:
             --localstatedir=/var
             --libdir=lib
             -Dglib_debug=enabled
-            -Dsystemtap=true
+            -Dsystemtap=enabled
             -Ddtrace=enabled
             -Dinstalled_tests=true
             -Dintrospection=enabled
@@ -796,7 +796,7 @@ scan-build:
             --prefix=$HOME/glib-installed
             --localstatedir=/var
             --libdir=lib
-            -Dsystemtap=true
+            -Dsystemtap=enabled
             -Ddtrace=enabled
             -Dinstalled_tests=true
             -Dintrospection=enabled

meson.build

@@ -2575,10 +2575,10 @@ if cc.has_header_symbol('sys/ptrace.h', 'PTRACE_O_EXITKILL')
 endif
 
 # systemtap
-want_systemtap = get_option('systemtap')
-enable_systemtap = false
+systemtap = get_option('systemtap').require(enable_dtrace, error_message: 'Cannot enable systemtap because dtrace feature is disabled')
+enable_systemtap = systemtap.allowed()
 
-if want_systemtap and enable_dtrace
+if enable_systemtap
   tapset_install_dir = get_option('tapset_install_dir')
   if tapset_install_dir == ''
     tapset_install_dir = join_paths(get_option('datadir'), 'systemtap/tapset', host_machine.cpu_family())
@@ -2587,7 +2587,6 @@ if want_systemtap and enable_dtrace
   stp_cdata.set('ABS_GLIB_RUNTIME_LIBDIR', glib_libdir)
   stp_cdata.set('LT_CURRENT', minor_version * 100)
   stp_cdata.set('LT_REVISION', micro_version)
-  enable_systemtap = true
 endif
 
 # introspection

meson_options.txt

@@ -56,8 +56,9 @@ option('dtrace',
        description : 'include tracing support for dtrace')
 
 option('systemtap',
-       type : 'boolean',
-       value : false,
+       type : 'feature',
+       value : 'auto',
+       deprecated : { 'true': 'enabled', 'false': 'disabled' },
        description : 'include tracing support for systemtap')
 
 option('tapset_install_dir',