Add a way to disable openthread in build_examples.py

This enables a build that has no runtime dependencies other than libc:

 0x0000000000000001 (NEEDED)             Shared library: [libdl.so.2]
 0x0000000000000001 (NEEDED)             Shared library: [libpthread.so.0]
 0x0000000000000001 (NEEDED)             Shared library: [librt.so.1]
 0x0000000000000001 (NEEDED)             Shared library: [libm.so.6]
 0x0000000000000001 (NEEDED)             Shared library: [libc.so.6]

This makes it easy to deploy on embedded Linux without installing other
libraries.

Tested via

 ./scripts/build/build_examples.py --target linux-arm64-chip-tool-ipv6only-no-ble-no-wifi-no-thread-asan-clang build
 ./scripts/build/build_examples.py --target linux-arm64-all-clusters-ipv6only-no-ble-no-wifi-no-thread-asan-clang build

examples/all-clusters-app/linux/main-common.cpp

@@ -32,6 +32,7 @@
 #include <new>
 #include <platform/DiagnosticDataProvider.h>
 #include <platform/PlatformManager.h>
+#include <signal.h>
 #include <system/SystemPacketBuffer.h>
 #include <transport/SessionManager.h>
 #include <transport/raw/PeerAddress.h>

scripts/build/build/targets.py

@@ -270,6 +270,7 @@ def HostTargets():
     builder.AppendVariant(name="ipv6only", enable_ipv4=False),
     builder.AppendVariant(name="no-ble", enable_ble=False),
     builder.AppendVariant(name="no-wifi", enable_wifi=False),
+    builder.AppendVariant(name="no-thread", enable_thread=False),
     builder.AppendVariant(name="tsan", conflicts=['asan'], use_tsan=True),
     builder.AppendVariant(name="asan", conflicts=['tsan'], use_asan=True),
     builder.AppendVariant(name="libfuzzer", requires=[
@@ -279,6 +280,7 @@ def HostTargets():
 
     builder.WhitelistVariantNameForGlob('no-interactive-ipv6only')
     builder.WhitelistVariantNameForGlob('ipv6only')
+    builder.WhitelistVariantNameForGlob('ipv6only-no-ble-no-wifi-no-thread-clang')
 
     for target in app_targets:
         if ('-rpc-console' in target.name) or ('-python-bindings' in target.name) or ('nl-test-runner' in target.name):

scripts/build/builders/host.py

@@ -192,9 +192,11 @@ def PlatformName(self):
 
 class HostBuilder(GnBuilder):
 
-    def __init__(self, root, runner, app: HostApp, board=HostBoard.NATIVE, enable_ipv4=True,
-                 enable_ble=True, enable_wifi=True, use_tsan=False,  use_asan=False, separate_event_loop=True,
-                 use_libfuzzer=False, use_clang=False, interactive_mode=True, extra_tests=False,
+    def __init__(self, root, runner, app: HostApp, board=HostBoard.NATIVE,
+                 enable_ipv4=True, enable_ble=True, enable_wifi=True,
+                 enable_thread=True, use_tsan=False, use_asan=False,
+                 separate_event_loop=True, use_libfuzzer=False, use_clang=False,
+                 interactive_mode=True, extra_tests=False,
                  use_platform_mdns=False, enable_rpcs=False):
         super(HostBuilder, self).__init__(
             root=os.path.join(root, 'examples', app.ExamplePath()),
@@ -216,6 +218,9 @@ def __init__(self, root, runner, app: HostApp, board=HostBoard.NATIVE, enable_ip
         if not enable_wifi:
             self.extra_gn_options.append('chip_enable_wifi=false')
 
+        if not enable_thread:
+            self.extra_gn_options.append('chip_enable_openthread=false')
+
         if use_tsan:
             self.extra_gn_options.append('is_tsan=true')