[stdlib] Buildfix differentiation for OpenBSD.

New files were added in #30875 which did not include os(OpenBSD), so add
this.

add_swift_target_library in AddSwiftStdlib subsequently required
modification. _add_target_variant_link_flags likely needs modification as
well, but this is better suited to a separate PR.

Author: 3405691582

stdlib/cmake/modules/AddSwiftStdlib.cmake

@@ -1399,6 +1399,9 @@ endfunction()
 # SWIFT_MODULE_DEPENDS_FREEBSD
 #   Swift modules this library depends on when built for FreeBSD.
 #
+# SWIFT_MODULE_DEPENDS_OPENBSD
+#   Swift modules this library depends on when built for OpenBSD.
+#
 # SWIFT_MODULE_DEPENDS_LINUX
 #   Swift modules this library depends on when built for Linux.
 #
@@ -1518,6 +1521,7 @@ function(add_swift_target_library name)
         SWIFT_MODULE_DEPENDS
         SWIFT_MODULE_DEPENDS_CYGWIN
         SWIFT_MODULE_DEPENDS_FREEBSD
+        SWIFT_MODULE_DEPENDS_OPENBSD
         SWIFT_MODULE_DEPENDS_HAIKU
         SWIFT_MODULE_DEPENDS_IOS
         SWIFT_MODULE_DEPENDS_LINUX
@@ -1676,6 +1680,9 @@ function(add_swift_target_library name)
     elseif(${sdk} STREQUAL FREEBSD)
       list(APPEND swiftlib_module_depends_flattened
            ${SWIFTLIB_SWIFT_MODULE_DEPENDS_FREEBSD})
+    elseif(${sdk} STREQUAL OPENBSD)
+      list(APPEND swiftlib_module_depends_flattened
+           ${SWIFTLIB_SWIFT_MODULE_DEPENDS_OPENBSD})
     elseif(${sdk} STREQUAL LINUX OR ${sdk} STREQUAL ANDROID)
       list(APPEND swiftlib_module_depends_flattened
            ${SWIFTLIB_SWIFT_MODULE_DEPENDS_LINUX})

stdlib/public/Differentiation/CMakeLists.txt

@@ -28,6 +28,7 @@ add_swift_target_library(swift_Differentiation ${SWIFT_STDLIB_LIBRARY_BUILD_TYPE
   SWIFT_MODULE_DEPENDS_WATCHOS Darwin
   SWIFT_MODULE_DEPENDS_LINUX Glibc
   SWIFT_MODULE_DEPENDS_FREEBSD Glibc
+  SWIFT_MODULE_DEPENDS_OPENBSD Glibc
   SWIFT_MODULE_DEPENDS_CYGWIN Glibc
   SWIFT_MODULE_DEPENDS_HAIKU Glibc
   SWIFT_MODULE_DEPENDS_WINDOWS MSVCRT

stdlib/public/Differentiation/TgmathDerivatives.swift.gyb

@@ -16,7 +16,7 @@ import Swift
 
 #if os(macOS) || os(iOS) || os(tvOS) || os(watchOS)
   import Darwin.C.tgmath
-#elseif os(Linux) || os(FreeBSD) || os(PS4) || os(Android) || os(Cygwin) || os(Haiku)
+#elseif os(Linux) || os(FreeBSD) || os(OpenBSD) || os(PS4) || os(Android) || os(Cygwin) || os(Haiku)
   import Glibc
 #elseif os(Windows)
   import MSVCRT