host/firmware/tools: Update minimum CMake versions

Various sub-projects around the UHD repository specify their own minimum
CMake versions (independent of UHD). We modify the minimum CMake
versions in the following way:

- All CMake files under firmware/ are bumped from 2.6 to 3.5. This is to
  allow newer CMake versions to work with these files (CMake 4 and
  beyond do no longer work if the minimum version is below 3.5). However,
  note that these CMake files are so simple they will keep working with
  older CMake versions, but that will require manually demoting the
  minimum version. Because more people are using CMake versions newer
  than 3.5 (especially with recent checkouts of UHD), this seems the
  more compatible solution.
- The CMake files for extension_example and init_usrp are bumped to
  3.12. This matches the version that UHD uses, which increases
  compatibility.

firmware/fx2/CMakeLists.txt

@@ -15,7 +15,9 @@
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #
 
-cmake_minimum_required(VERSION 2.6)
+# In a pinch, this will work with older CMake versions too (down to 2.6),
+# but we set it to 3.5 to also work with newer CMake versions (4 and above).
+cmake_minimum_required(VERSION 3.5)
 set(CMAKE_TOOLCHAIN_FILE ${CMAKE_SOURCE_DIR}/config/Toolchain-sdcc.cmake)
 project(USRP1 C)
 set(CMAKE_MODULE_PATH ${CMAKE_MODULE_PATH} "${CMAKE_SOURCE_DIR}/config/")

firmware/octoclock/CMakeLists.txt

@@ -15,7 +15,9 @@
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #
 
-cmake_minimum_required(VERSION 2.6)
+# In a pinch, this will work with older CMake versions too (down to 2.6),
+# but we set it to 3.5 to also work with newer CMake versions (4 and above).
+cmake_minimum_required(VERSION 3.5)
 set(CMAKE_SYSTEM_NAME Generic)
 
 find_program(AVR_CC avr-gcc REQUIRED)

firmware/usrp2/CMakeLists.txt

@@ -18,7 +18,9 @@
 ########################################################################
 # setup project and compiler
 ########################################################################
-cmake_minimum_required(VERSION 2.6)
+# In a pinch, this will work with older CMake versions too (down to 2.6),
+# but we set it to 3.5 to also work with newer CMake versions (4 and above).
+cmake_minimum_required(VERSION 3.5)
 #force the compiler because the check wont use the special flag below
 include(CMakeForceCompiler)
 set(CMAKE_SYSTEM_NAME Generic)

firmware/usrp3/CMakeLists.txt

@@ -18,7 +18,9 @@
 ########################################################################
 # setup project and compiler
 ########################################################################
-cmake_minimum_required(VERSION 2.6)
+# In a pinch, this will work with older CMake versions too (down to 2.6),
+# but we set it to 3.5 to also work with newer CMake versions (4 and above).
+cmake_minimum_required(VERSION 3.5)
 #force the compiler because the check wont use the special flag below
 include(CMakeForceCompiler)
 set(CMAKE_SYSTEM_NAME Generic)

host/examples/extension_example/CMakeLists.txt

@@ -5,7 +5,7 @@
 # SPDX-License-Identifier: GPL-3.0-or-later
 #
 
-cmake_minimum_required(VERSION 3.5.1)
+cmake_minimum_required(VERSION 3.12)
 project(EXTENSION_EXAMPLE CXX)
 
 ### Configure Compiler ########################################################

tools/dissectors/CMakeLists.txt

@@ -4,7 +4,7 @@
 # SPDX-License-Identifier: GPL-3.0-or-later
 #
 
-cmake_minimum_required(VERSION 3.1)
+cmake_minimum_required(VERSION 3.5)
 cmake_policy(SET CMP0048 NEW)
 project(EttusDissectors VERSION 4.0.0 DESCRIPTION "Dissector Plugins" LANGUAGES C CXX)