package/gdb: handle xxhash optional dependency

Since gdb 9.x, gdb can optionally use the xxhash library. Since we
currently don't do anything about it, it's a potential "silent"
dependency.

In particular, for host-gdb, this means host-gdb might end up being
linked with the system-provided xxhash library if available.

This patch handles this dependency:

- For the target package, by looking at the value of
  BR2_PACKAGE_XXHASH

- For the host package, by looking at the value of a newly introduced
  BR2_PACKAGE_HOST_GDB_XXHASH

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/gdb/Config.in.host

@@ -49,6 +49,11 @@ config BR2_PACKAGE_HOST_GDB_LZMA
 	help
 	  This option enables lzma support in the cross gdb.
 
+config BR2_PACKAGE_HOST_GDB_XXHASH
+	bool "xxhash support"
+	help
+	  This option enables xxhash support in the cross gdb.
+
 choice
 	prompt "GDB debugger Version"
 	default BR2_GDB_VERSION_16

package/gdb/gdb.mk

@@ -217,6 +217,14 @@ else
 GDB_CONF_OPTS += --without-expat
 endif
 
+ifeq ($(BR2_PACKAGE_XXHASH),y)
+GDB_CONF_OPTS += --with-xxhash
+GDB_CONF_OPTS += --with-xxhash-prefix=$(STAGING_DIR)/usr
+GDB_DEPENDENCIES += xxhash
+else
+GDB_CONF_OPTS += --without-xxhash
+endif
+
 ifeq ($(BR2_PACKAGE_XZ),y)
 GDB_CONF_OPTS += --with-lzma
 GDB_CONF_OPTS += --with-liblzma-prefix=$(STAGING_DIR)/usr
@@ -301,6 +309,14 @@ else
 HOST_GDB_CONF_OPTS += --without-lzma
 endif
 
+ifeq ($(BR2_PACKAGE_HOST_GDB_XXHASH),y)
+HOST_GDB_CONF_OPTS += --with-xxhash
+HOST_GDB_CONF_OPTS += --with-xxhash-prefix=$(HOST_DIR)
+HOST_GDB_DEPENDENCIES += host-xxhash
+else
+HOST_GDB_CONF_OPTS += --without-xxhash
+endif
+
 # Since gdb 9, in-tree builds for GDB are not allowed anymore,
 # so we create a 'build' subdirectory in the gdb sources, and
 # build from there.