Fixes an compilation error when 'ONLY_C_LOCALE' is used to build the project.

Upstream-Bug: https://github.com/HowardHinnant/date/issues/589

--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -76,10 +76,25 @@ if (CMAKE_VERSION VERSION_GREATER_EQUAL 3.15)
     # public headers will get installed:
     set_target_properties( date PROPERTIES PUBLIC_HEADER include/date/date.h )
 endif ()
-target_compile_definitions( date INTERFACE
-    #To workaround libstdc++ issue https://github.com/HowardHinnant/date/issues/388
-    ONLY_C_LOCALE=$<IF:$<BOOL:${COMPILE_WITH_C_LOCALE}>,1,0>
-    $<$<BOOL:${DISABLE_STRING_VIEW}>:HAS_STRING_VIEW=0> )
+
+# These used to be set with generator expressions,
+#
+#   ONLY_C_LOCALE=$<IF:$<BOOL:${COMPILE_WITH_C_LOCALE}>,1,0>
+#
+# which expand in the output target file to, e.g.
+#
+#   ONLY_C_LOCALE=$<IF:$<BOOL:FALSE>,1,0>
+#
+# This string is then (somtimes?) not correctly interpreted.
+if ( COMPILE_WITH_C_LOCALE )
+  # To workaround libstdc++ issue https://github.com/HowardHinnant/date/issues/388
+  target_compile_definitions( date INTERFACE ONLY_C_LOCALE=1 )
+else()
+  target_compile_definitions( date INTERFACE ONLY_C_LOCALE=0 )
+endif()
+if ( DISABLE_STRING_VIEW )
+  target_compile_definitions( date INTERFACE HAS_STRING_VIEW=0 )
+endif()
 
 #[===================================================================[
    tz (compiled) library
@@ -89,27 +104,40 @@ if( BUILD_TZ_LIB )
     target_sources( date-tz
       PUBLIC
         $<BUILD_INTERFACE:${CMAKE_CURRENT_LIST_DIR}/include>$<INSTALL_INTERFACE:include>/date/tz.h
-        $<$<BOOL:${IOS}>:$<BUILD_INTERFACE:${CMAKE_CURRENT_LIST_DIR}/include>$<INSTALL_INTERFACE:include>/date/ios.h>
       PRIVATE
         include/date/tz_private.h
-        $<$<BOOL:${IOS}>:src/ios.mm>
         src/tz.cpp )
+    if ( IOS )
+      target_sources( date-tz
+        PUBLIC
+          $<BUILD_INTERFACE:${CMAKE_CURRENT_LIST_DIR}/include>$<INSTALL_INTERFACE:include>/date/ios.h
+        PRIVATE
+          src/ios.mm )
+    endif()
     add_library( date::tz ALIAS date-tz )
     target_link_libraries( date-tz PUBLIC date )
     target_include_directories( date-tz PUBLIC
         $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>
         $<INSTALL_INTERFACE:include> )
-    target_compile_definitions( date-tz
-        PRIVATE
-            AUTO_DOWNLOAD=$<IF:$<OR:$<BOOL:${USE_SYSTEM_TZ_DB}>,$<BOOL:${MANUAL_TZ_DB}>>,0,1>
-            HAS_REMOTE_API=$<IF:$<OR:$<BOOL:${USE_SYSTEM_TZ_DB}>,$<BOOL:${MANUAL_TZ_DB}>>,0,1>
-            $<$<AND:$<BOOL:${WIN32}>,$<BOOL:${BUILD_SHARED_LIBS}>>:DATE_BUILD_DLL=1>
-            $<$<BOOL:${USE_TZ_DB_IN_DOT}>:INSTALL=.>
-        PUBLIC
-            USE_OS_TZDB=$<IF:$<AND:$<BOOL:${USE_SYSTEM_TZ_DB}>,$<NOT:$<BOOL:${WIN32}>>,$<NOT:$<BOOL:${MANUAL_TZ_DB}>>>,1,0>
-        INTERFACE
-            $<$<AND:$<BOOL:${WIN32}>,$<BOOL:${BUILD_SHARED_LIBS}>>:DATE_USE_DLL=1> )
+
+    if ( USE_SYSTEM_TZ_DB OR MANUAL_TZ_DB )
+      target_compile_definitions( date-tz PRIVATE AUTO_DOWNLOAD=0 HAS_REMOTE_API=0 )
+    else()
+      target_compile_definitions( date-tz PRIVATE AUTO_DOWNLOAD=1 HAS_REMOTE_API=1 )
+    endif()
+
+    if ( USE_SYSTEM_TZ_DB AND NOT WIN32 AND NOT MANUAL_TZ_DB )
+      target_compile_definitions( date-tz PRIVATE INSTALL=. PUBLIC USE_OS_TZDB=1 )
+    else()
+      target_compile_definitions( date-tz PUBLIC USE_OS_TZDB=0 )
+    endif()
+
+    if ( WIN32 AND BUILD_SHARED_LIBS )
+      target_compile_definitions( date-tz PUBLIC DATE_BUILD_DLL=1 )
+    endif()
+
     set(TZ_HEADERS include/date/tz.h)
+
     if( IOS )
         list(APPEND TZ_HEADERS include/date/ios.h)
     endif( )
--