Emscripten: Put back -gseparate-dwarf

...which had been replaced with -gsplit-dwarf in
8ecdff7ac3 "Modernize wasm debug symbol
generation".  But -gseparate-dwarf and -gsplit-dwarf are apparently orthogonal:

-gseparate-dwarf adds a supplementary *.wasm.debug.wasm (whose relative URL is
recorded in an external_debug_info section in the original *.wasm), and the
original *.wasm and the supplementary *.wasm.debug.wasm have exactly the same
content, except that only the supplementary *.wasm.debug.wasm contains any of
the .debug_* sections (and only the original *.wasm contains the
external_debug_info section).  That way, the original *.wasm stays small (so
that it does not exceed any limits of the browser's JS WebAssembly instantiation
machinery), while the browser's debugger (like Chrome's "C/C++ DevTools Support
(DWARF)" extension) uses the supplementary *.wasm.debug.wasm.  This is
especially relevant when building LO with e.g. -fsanitize=address, where the
resulting soffice.wasm would otherwise easily grow too large.

-gsplit-dwarf, on the other hand, leaves certain debug information in .debug_*
sections in the original *.wasm and offloads further debug data to an auxiliary
*.wasm.dwp (which the browser's debugger will then load and use in addition to
using the original *.wasm's debug information).  When combined with
-gseparate-dwarf, there's an overall three files now: the original *.wasm (used
by the browser's JS WebAssembly instantiation machinery; lacking any debug
information), the supplementary *.wasm.debug.wasm (used by the browser's
debugger; containing some debug information), and the auxiliary
*.wasm.debug.wasm.dwp (used by the browser's debugger; containing further debug
information).  (One might assume that when using -gseparate-dwarf there would be
no benefit from additionally using -gsplit-dwarf.  But when I tried that with at
least Chrome version 138.0.7204.100 and the "C/C++ DevTools Support (DWARF)"
extension version 0.2.5854.1, it would still sometimes fail with

> [C/C++ DevTools Support (DWARF)] Loading debug symbols for http://localhost:6931/soffice.wasm (via soffice.wasm.debug.wasm)…
> [C/C++ DevTools Support (DWARF)] Failed to load debug symbols for http://localhost:6931/soffice.wasm (TypeError: Failed to fetch)

and the emrun server reporting

> 127.0.0.1 - - [15/Jul/2025 22:41:58] code 404, message File not found: /home/sberg/cowasm/core/workdir/installation/LibreOffice/emscripten/soffice.wasm.debug.wasm.dwp
> 127.0.0.1 - - [15/Jul/2025 22:41:58] "GET /soffice.wasm.debug.wasm.dwp HTTP/1.1" 404 -

making it look like it wanted to access a non-existing auxiliary
soffice.wasm.debug.wasm.dwp for some unclear reason.  So, at least for now, it
looks better to just use a setup that provides that auxiliary file anyway.)

Change-Id: I72352479c864c8d89cc63cc228aa676c7c2d8ccf
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/187953
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <stephan.bergmann@collabora.com>

configure.ac

@@ -5178,7 +5178,7 @@ if test "$enable_split_debug" != no; then
     fi
     if test -n "$use_split_debug"; then
         if test "$_os" = "Emscripten"; then
-            TEST_CC_FLAG='-gsplit-dwarf -gpubnames'
+            TEST_CC_FLAG='-gseparate-dwarf -gsplit-dwarf -gpubnames'
         else
             TEST_CC_FLAG=-gsplit-dwarf
         fi

instsetoo_native/CustomTarget_emscripten-install.mk

@@ -19,7 +19,9 @@ emscripten_install_files := \
     soffice.js \
     soffice.wasm \
     $(if $(EMSCRIPTEN_WORKERJS),soffice.worker.js) \
-    $(if $(ENABLE_SYMBOLS_FOR),soffice.wasm.dwp) \
+    $(if $(ENABLE_SYMBOLS_FOR), \
+        soffice.wasm.debug.wasm \
+        soffice.wasm.debug.wasm.dwp) \
     $(if $(DISABLE_GUI),, \
         qt_soffice.html \
         qtloader.js \

solenv/gbuild/platform/EMSCRIPTEN_INTEL_GCC.mk

@@ -76,7 +76,7 @@ gb_LINKERSTRIPDEBUGFLAGS :=
 gb_DEBUGINFO_FLAGS = -g
 
 ifeq ($(HAVE_EXTERNAL_DWARF),TRUE)
-gb_DEBUGINFO_FLAGS += -gsplit-dwarf -gpubnames
+gb_DEBUGINFO_FLAGS += -gseparate-dwarf -gsplit-dwarf -gpubnames
 endif
 
 gb_COMPILEROPTFLAGS := -O3
@@ -92,7 +92,8 @@ $(call gb_LinkTarget_add_auxtargets,$(2),\
         $(patsubst %.lib,%.linkdeps,$(3)) \
         $(patsubst %.lib,%.wasm,$(3)) \
         $(if $(EMSCRIPTEN_WORKERJS),$(patsubst %.lib,%.worker.js,$(3))) \
-        $(patsubst %.lib,%.wasm.dwp,$(3)) \
+        $(patsubst %.lib,%.wasm.debug.wasm,$(3)) \
+        $(patsubst %.lib,%.wasm.debug.wasm.dwp,$(3)) \
 )
 
 endef
@@ -102,7 +103,8 @@ $(call gb_LinkTarget_add_auxtargets,$(2),\
         $(patsubst %.lib,%.linkdeps,$(3)) \
         $(patsubst %.lib,%.wasm,$(3)) \
         $(if $(EMSCRIPTEN_WORKERJS),$(patsubst %.lib,%.worker.js,$(3))) \
-        $(patsubst %.lib,%.wasm.dwp,$(3)) \
+        $(patsubst %.lib,%.wasm.debug.wasm,$(3)) \
+        $(patsubst %.lib,%.wasm.debug.wasm.dwp,$(3)) \
 )
 
 endef

solenv/gbuild/platform/unxgcc.mk

@@ -172,7 +172,7 @@ $(call gb_Helper_abbreviate_dirs,\
                 ) \
 		-o $(1) \
 	$(if $(SOVERSIONSCRIPT),&& ln -sf ../../program/$(notdir $(1)) $(ILIBTARGET)) \
-	$(if $(filter EMSCRIPTEN,$(OS)),$(if $(filter TRUE,$(HAVE_EXTERNAL_DWARF)),&& emdwp -e $(patsubst %$(gb_Executable_EXT),%.wasm,$(1)) -o $(patsubst %$(gb_Executable_EXT),%.wasm.dwp,$(1)))) \
+	$(if $(filter EMSCRIPTEN,$(OS)),$(if $(filter TRUE,$(HAVE_EXTERNAL_DWARF)),&& emdwp -e $(patsubst %$(gb_Executable_EXT),%.wasm.debug.wasm,$(1)) -o $(patsubst %$(gb_Executable_EXT),%.wasm.debug.wasm.dwp,$(1)))) \
 	$(if $(call gb_LinkTarget__WantLock,$(2)),; RC=$$? ; rm -f $(gb_LinkTarget__Lock); if test $$RC -ne 0; then exit $$RC; fi))
 
 $(if $(filter Library,$(TARGETTYPE)), $(call gb_Helper_abbreviate_dirs,\