Pass -enable-library-evolution for PackageDescription/Plugin in Linux (#6157)

Reverts 1998284 / #3526

Related to SR-14718 (#4416).

Since #3526 was merged, #5874 tried to apply the original idea of using
`@_implementationOnly Foundation` in PackageDescription/Plugin to avoid
leaking `Foundation` into the manifests.

Author: drodriguez

Package.swift

@@ -158,7 +158,7 @@ let package = Package(
             exclude: ["CMakeLists.txt"],
             swiftSettings: [
                 .unsafeFlags(["-package-description-version", "999.0"]),
-                .unsafeFlags(["-enable-library-evolution"], .when(platforms: [.macOS]))
+                .unsafeFlags(["-enable-library-evolution"]),
             ]
         ),
 
@@ -170,7 +170,7 @@ let package = Package(
             exclude: ["CMakeLists.txt"],
             swiftSettings: [
                 .unsafeFlags(["-package-description-version", "999.0"]),
-                .unsafeFlags(["-enable-library-evolution"], .when(platforms: [.macOS]))
+                .unsafeFlags(["-enable-library-evolution"]),
             ]
         ),
 

Sources/PackageDescription/CMakeLists.txt

@@ -25,10 +25,10 @@ add_library(PackageDescription
 
 target_compile_options(PackageDescription PUBLIC
   $<$<COMPILE_LANGUAGE:Swift>:-package-description-version$<SEMICOLON>999.0>)
+target_compile_options(PackageDescription PUBLIC
+  $<$<COMPILE_LANGUAGE:Swift>:-enable-library-evolution>)
 
 if(CMAKE_HOST_SYSTEM_NAME STREQUAL Darwin)
-  target_compile_options(PackageDescription PUBLIC
-    $<$<COMPILE_LANGUAGE:Swift>:-enable-library-evolution>)
   set(SWIFT_INTERFACE_PATH ${CMAKE_BINARY_DIR}/pm/ManifestAPI/PackageDescription.swiftinterface)
   target_compile_options(PackageDescription PUBLIC
     $<$<COMPILE_LANGUAGE:Swift>:-emit-module-interface-path$<SEMICOLON>${SWIFT_INTERFACE_PATH}>)

Sources/PackagePlugin/CMakeLists.txt

@@ -23,10 +23,10 @@ add_library(PackagePlugin SHARED
 
 target_compile_options(PackagePlugin PUBLIC
   $<$<COMPILE_LANGUAGE:Swift>:-package-description-version$<SEMICOLON>999.0>)
+target_compile_options(PackagePlugin PUBLIC
+  $<$<COMPILE_LANGUAGE:Swift>:-enable-library-evolution>)
 
 if(CMAKE_HOST_SYSTEM_NAME STREQUAL Darwin)
-  target_compile_options(PackagePlugin PUBLIC
-    $<$<COMPILE_LANGUAGE:Swift>:-enable-library-evolution>)
   set(SWIFT_INTERFACE_PATH ${CMAKE_BINARY_DIR}/pm/PluginAPI/PackagePlugin.swiftinterface)
   target_compile_options(PackagePlugin PUBLIC
     $<$<COMPILE_LANGUAGE:Swift>:-emit-module-interface-path$<SEMICOLON>${SWIFT_INTERFACE_PATH}>)