updated build system (#484)

* updated build system

* set relative path for exprtk
* set optimisation flags to max '-O2' to alleviate CI build times
* set absolute hash for pmt dependency

N.B. performance difference between `-O2` vs. '-03' proved to be insignificant.

Signed-off-by: rstein <r.steinhagen@gsi.de>

CMakeLists.txt

@@ -75,9 +75,14 @@ if(CMAKE_CXX_COMPILER_ID MATCHES "(Clang|GNU|Intel)")
 
   # Add a build type that keeps runtime checks enabled
   set(CMAKE_CXX_FLAGS_RELWITHASSERT
-      "-O3"
+      "-O2"
       CACHE INTERNAL "Flags used by the compiler during release builds containing runtime checks.")
 
+  # Add a build type that keeps runtime checks enabled
+  set(CMAKE_CXX_FLAGS_RELEASE
+      "-O2"
+      CACHE INTERNAL "Flags used by the compiler during release builds.")
+
   # The default value is often an empty string, but this is usually not desirable and one of the other standard build
   # types is usually more appropriate.
   if(NOT CMAKE_BUILD_TYPE)
@@ -223,22 +228,18 @@ endif()
 # include header-only libraries that have been inlined to simplify builds w/o requiring access to the internet
 if(NOT (TARGET magic_enum))
   add_library(magic_enum INTERFACE)
-  target_include_directories(magic_enum ${CMAKE_EXT_DEP_WARNING_GUARD} INTERFACE ${PROJECT_SOURCE_DIR}/third_party/magic_enum/)
+  target_include_directories(magic_enum ${CMAKE_EXT_DEP_WARNING_GUARD}
+                             INTERFACE ${PROJECT_SOURCE_DIR}/third_party/magic_enum/)
 endif()
 
 # include exprtk header-only libraries available as a statically linked library to simplify/speed-up builds
-include_directories("${CMAKE_SOURCE_DIR}/third_party")
-include_directories("${CMAKE_SOURCE_DIR}/third_party/exprtk")
-add_library(exprtk STATIC
-        "${CMAKE_SOURCE_DIR}/third_party/exprtk.cpp" # dummy source file
-        "${CMAKE_SOURCE_DIR}/third_party/exprtk.hpp"
+add_library(
+  exprtk STATIC "${CMAKE_CURRENT_SOURCE_DIR}/third_party/exprtk.hpp"
+                "${CMAKE_CURRENT_SOURCE_DIR}/third_party/exprtk.cpp" # dummy source file
 )
-target_sources(exprtk PRIVATE "${CMAKE_SOURCE_DIR}/third_party/exprtk.hpp")
-target_include_directories(exprtk PUBLIC
-        "${CMAKE_SOURCE_DIR}/third_party"
-        "${CMAKE_SOURCE_DIR}/third_party/exprtk"
-)
-target_compile_options(exprtk PRIVATE -O3)
+target_include_directories(exprtk PUBLIC "${CMAKE_CURRENT_SOURCE_DIR}/third_party"
+                                         "${CMAKE_CURRENT_SOURCE_DIR}/third_party/exprtk")
+target_compile_options(exprtk PRIVATE -O1)
 # include exprtk header-only - END
 
 include(FetchContent)
@@ -250,7 +251,8 @@ FetchContent_Declare(
 FetchContent_Declare(
   pmt
   GIT_REPOSITORY https://github.com/gnuradio/pmt.git
-  GIT_TAG main)
+  GIT_TAG e1a46cb61decb044f6ab0a58a77211beb3630340 # latest as of 2023-12-06
+)
 
 FetchContent_Declare(
   ut