Renamed the patch and updated comment, as I had the logic inverted.

pkgs/applications/radio/pothos/cstring.patch

@@ -0,0 +1,50 @@
+Submodule blocks contains modified content
+diff --git a/blocks/file/BinaryFileSink.cpp b/blocks/file/BinaryFileSink.cpp
+index 31c9a41..0083b0d 100644
+--- a/blocks/file/BinaryFileSink.cpp
++++ b/blocks/file/BinaryFileSink.cpp
+@@ -13,6 +13,7 @@
+ #endif //_MSC_VER
+ #include <stdio.h>
+ #include <cerrno>
++#include <cstring>
+
+ #ifndef O_BINARY
+ #define O_BINARY 0
+diff --git a/blocks/file/BinaryFileSource.cpp b/blocks/file/BinaryFileSource.cpp
+index 0151231..379d383 100644
+--- a/blocks/file/BinaryFileSource.cpp
++++ b/blocks/file/BinaryFileSource.cpp
+@@ -13,6 +13,7 @@
+ #endif //_MSC_VER
+ #include <stdio.h>
+ #include <cerrno>
++#include <cstring>
+
+ #ifndef O_BINARY
+ #define O_BINARY 0
+diff --git a/blocks/file/TextFileSink.cpp b/blocks/file/TextFileSink.cpp
+index b4b2f08..2be66e2 100644
+--- a/blocks/file/TextFileSink.cpp
++++ b/blocks/file/TextFileSink.cpp
+@@ -6,6 +6,7 @@
+ #include <complex>
+ #include <fstream>
+ #include <cerrno>
++#include <cstring>
+
+ /***********************************************************************
+  * |PothosDoc Text File Sink
+Submodule soapy contains modified content
+diff --git a/soapy/DemoController.cpp b/soapy/DemoController.cpp
+index 4ce8ead..9a4e742 100644
+--- a/soapy/DemoController.cpp
++++ b/soapy/DemoController.cpp
+@@ -6,6 +6,7 @@
+ #include <iostream>
+ #include <chrono>
+ #include <algorithm> //min/max
++#include <cstring>
+
+ /***********************************************************************
+  * |PothosDoc SDR Demo Controller

pkgs/applications/radio/pothos/default.nix

@@ -41,8 +41,13 @@ mkDerivation rec {
       url = "https://github.com/pothosware/PothosCore/commit/092d1209b0fd0aa8a1733706c994fa95e66fd017.patch";
       hash = "sha256-bZXG8kD4+1LgDV8viZrJ/DMjg8UvW7b5keJQDXurfkA=";
     })
+    # various source files are missing imports of <cstring>
+    ./cstring.patch
   ];
 
+  # poco 1.14 requires c++17
+  NIX_CFLAGS_COMPILE = [ "-std=gnu++17" ];
+
   nativeBuildInputs = [
     cmake
     pkg-config

pkgs/by-name/po/poco/disable-internal-pcre-files-for-static-builds.patch

@@ -0,0 +1,23 @@
+diff --git a/Foundation/CMakeLists.txt b/Foundation/CMakeLists.txt
+index d5f3b267d..dfaf99a10 100644
+--- a/Foundation/CMakeLists.txt
++++ b/Foundation/CMakeLists.txt
+@@ -31,11 +31,13 @@ if(POCO_UNBUNDLED)
+ 	find_package(ZLIB REQUIRED)
+ 	find_package(Utf8Proc REQUIRED)
+
+-	#HACK: Unicode.cpp requires functions from these files. The can't be taken from the library
+-	POCO_SOURCES(SRCS RegExp
+-		src/pcre2_ucd.c
+-		src/pcre2_tables.c
+-	)
++    if(NOT POCO_STATIC AND BUILD_SHARED_LIBS)
++    	#HACK: Unicode.cpp requires functions from these files. The can't be taken from the library
++    	POCO_SOURCES(SRCS RegExp
++    		src/pcre2_ucd.c
++    		src/pcre2_tables.c
++        )
++    endif()
+
+ else()
+ 	# pcre2

pkgs/by-name/po/poco/package.nix

@@ -10,18 +10,19 @@
   sqlite,
   openssl,
   unixODBC,
+  utf8proc,
   libmysqlclient,
 }:
 
 stdenv.mkDerivation rec {
   pname = "poco";
 
-  version = "1.13.3";
+  version = "1.14.1";
 
   src = fetchFromGitHub {
     owner = "pocoproject";
     repo = "poco";
-    sha256 = "sha256-ryBQjzg1DyYd/LBZzjHxq8m/7ZXRSKNNGRkIII0eHK0=";
+    hash = "sha256-acq2eja61sH/QHwMPmiDNns2jvXRTk0se/tHj9XRSiU=";
     rev = "poco-${version}-release";
   };
 
@@ -32,8 +33,10 @@ stdenv.mkDerivation rec {
 
   buildInputs = [
     unixODBC
+    utf8proc
     libmysqlclient
   ];
+
   propagatedBuildInputs = [
     zlib
     pcre2
@@ -50,8 +53,15 @@ stdenv.mkDerivation rec {
   MYSQL_DIR = libmysqlclient;
   MYSQL_INCLUDE_DIR = "${MYSQL_DIR}/include/mysql";
 
-  configureFlags = [
-    "--unbundled"
+  cmakeFlags = [
+    # use nix provided versions of sqlite, zlib, pcre, expat, ... instead of bundled versions
+    "-DPOCO_UNBUNDLED=ON"
+  ];
+
+  patches = [
+    # poco builds its own version of pcre, disable it for static builds
+    # https://github.com/pocoproject/poco/issues/4871
+    ./disable-internal-pcre-files-for-static-builds.patch
   ];
 
   postFixup = ''