Use spdlog::spdlog_header_only

Switch to the header-only version of spdlog, since MacPorts currently ships
a precompiled spdlog.a that contains symbols compatible with fmt8, but we're
using fmt9.

Upstream-Status: Inappropriate [configuration]

--- ./source/libmain/CMakeLists.txt.orig	2023-02-15 10:13:28.000000000 +0100
+++ ./source/libmain/CMakeLists.txt	2023-02-15 10:14:46.000000000 +0100
@@ -12,4 +12,4 @@
         result_a
         flags_a
         fmt::fmt
-        spdlog::spdlog)
+        spdlog::spdlog_header_only)
--- ./source/bear/CMakeLists.txt.orig	2023-02-15 10:13:28.000000000 +0100
+++ ./source/bear/CMakeLists.txt	2023-02-15 10:14:23.000000000 +0100
@@ -14,7 +14,7 @@
         fmt::fmt
         citnames_a
         intercept_a
-        spdlog::spdlog)
+        spdlog::spdlog_header_only)
 
 # Create an executable from the sub projects.
 add_executable(bear
--- ./source/citnames/CMakeLists.txt.orig	2023-02-15 10:13:28.000000000 +0100
+++ ./source/citnames/CMakeLists.txt	2023-02-15 10:14:33.000000000 +0100
@@ -12,7 +12,7 @@
         shell_a
         sys_a
         fmt::fmt
-        spdlog::spdlog
+        spdlog::spdlog_header_only
         nlohmann_json::nlohmann_json)
 target_compile_options(citnames_json_a PRIVATE -fexceptions)
 
@@ -44,7 +44,7 @@
         sys_a
         exec_a
         fmt::fmt
-        spdlog::spdlog)
+        spdlog::spdlog_header_only)
 
 include(GNUInstallDirs)
 
--- ./source/intercept/CMakeLists.txt.orig	2023-02-15 10:13:28.000000000 +0100
+++ ./source/intercept/CMakeLists.txt	2023-02-15 10:14:43.000000000 +0100
@@ -51,7 +51,7 @@
         rpc_a
         sys_a
         result_a
-        spdlog::spdlog)
+        spdlog::spdlog_header_only)
 
 # Markdown file is the source to the man file. Please modify that and generate
 # the man file from it with pandoc.
@@ -82,7 +82,7 @@
         result_a
         sys_a
         rpc_a
-        spdlog::spdlog)
+        spdlog::spdlog_header_only)
 
 
 # Intercept report sender executable.
--- ./source/libsys/CMakeLists.txt.orig	2023-02-15 10:13:28.000000000 +0100
+++ ./source/libsys/CMakeLists.txt	2023-02-15 10:14:17.000000000 +0100
@@ -16,7 +16,7 @@
         ${CMAKE_DL_LIBS}
         result_a
         fmt::fmt
-        spdlog::spdlog)
+        spdlog::spdlog_header_only)
 
 if (ENABLE_UNIT_TESTS)
     add_executable(sys_unit_test