remove obsolete -single_module linker flag (is the default)

has already been unnecessary since over 15 years/was the default since
OS X 10.4 (2005) along with ignoring the corresponding altenative
(-multi_module) switch, from man ld:
-single_module
    This is now the default so does not need to be specified.

-multi_module
    Multi-modules in dynamic libraries have been ignored at runtime
    since Mac OS X 10.4.0.  This option is obsolete.

Xcode 15 now warns about it being obsolete, so remove it.

Change-Id: I4d4aab452a330c3c4ec97da4232c3af6350c0ff4
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/157407
Tested-by: Jenkins
Reviewed-by: Patrick Luby <plubius@neooffice.org>
Reviewed-by: Christian Lohmaier <lohmaier+LibreOffice@googlemail.com>

configure.ac

@@ -1002,7 +1002,7 @@ darwin*) # macOS
     INSTROOTCONTENTSUFFIX=/Contents
     SDKDIRNAME=${PRODUCTNAME_WITHOUT_SPACES}${PRODUCTVERSION}_SDK
     # See "Default values, as such probably valid just for Linux" comment above the case "$host_os"
-    LINKFLAGSSHL="-dynamiclib -single_module"
+    LINKFLAGSSHL="-dynamiclib"
 
     # -fPIC is default
     PICSWITCH=""
@@ -1043,7 +1043,7 @@ ios*) # iOS
         host=x86_64-apple-darwin
     fi
     # See "Default values, as such probably valid just for Linux" comment above the case "$host_os"
-    LINKFLAGSSHL="-dynamiclib -single_module"
+    LINKFLAGSSHL="-dynamiclib"
 
     # -fPIC is default
     PICSWITCH=""

odk/settings/settings.mk

@@ -469,7 +469,7 @@ CC_OUTPUT_SWITCH=-o
 
 LIBO_SDK_LDFLAGS_STDLIBS =
 
-LIBRARY_LINK_FLAGS=-dynamiclib -single_module -Wl,-multiply_defined,suppress $(GCC_ARCH_OPTION)
+LIBRARY_LINK_FLAGS=-dynamiclib -Wl,-multiply_defined,suppress $(GCC_ARCH_OPTION)
 
 # install_name '@executable_path$/(@:f)'
 COMP_LINK_FLAGS=$(LIBRARY_LINK_FLAGS)

solenv/gbuild/platform/macosx.mk

@@ -177,7 +177,7 @@ endef
 # Library class
 
 gb_Library_DEFS :=
-gb_Library_TARGETTYPEFLAGS := -dynamiclib -single_module
+gb_Library_TARGETTYPEFLAGS := -dynamiclib
 gb_Bundle_TARGETTYPEFLAGS := -bundle
 gb_Library_UDK_MAJORVER := 3
 gb_Library_SYSPRE := lib