[librsvg: 2/3] Add a dummy file, to make sure the library is non-empty

[Federico Mena Quintero <federico src gnome org>]

commit 8cea2b36244d4508d07d84440087c9c392b834ef
Author: Kleis Auke Wolthuizen <github kleisauke nl>
Date:   Wed Oct 16 09:54:03 2019 +0200

    Add a dummy file, to make sure the library is non-empty
    
    Should fix the macOS build.

 Makefile.am     |  6 +++---
 librsvg/dummy.c | 30 ++++++++++++++++++++++++++++++
 2 files changed, 33 insertions(+), 3 deletions(-)
---
diff --git a/Makefile.am b/Makefile.am
index a04828c9..b28ddd73 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -8,7 +8,7 @@ noinst_LTLIBRARIES = librsvg_c_api.la
 # This is empty, because automake wants to have a C sources list for
 # the LTLIBRARIES.  See LIBRSVG_INTERNALS_SRC below for the real list
 # of Rust sources.
-librsvg_c_api_la_SOURCES =
+librsvg_c_api_la_SOURCES = librsvg/dummy.c
 
 bin_PROGRAMS = rsvg-convert
 
@@ -182,7 +182,7 @@ dist-hook:
        mkdir .cargo &&                                                         \
        cp cargo-vendor-config .cargo/config)
 
-librsvg_c_api.la: $(LIBRSVG_INTERNALS_SRC) $(LIBRSVG_C_API_SRC)
+librsvg_c_api.la: $(librsvg_c_api_la_OBJECTS) $(LIBRSVG_INTERNALS_SRC) $(LIBRSVG_C_API_SRC)
        +cd $(top_srcdir)/librsvg &&                                            \
        PKG_CONFIG_ALLOW_CROSS=1                                                \
        PKG_CONFIG='$(PKG_CONFIG)'                                              \
@@ -191,7 +191,7 @@ librsvg_c_api.la: $(LIBRSVG_INTERNALS_SRC) $(LIBRSVG_C_API_SRC)
        && if [[ $$($(NM) -g $(RUST_LIB) | grep "T __*clzsi2" -c) -gt 1 ]] ; then \
                $(AR) d $(RUST_LIB) clzsi2.o;                                   \
        fi \
-       && cd $(LIBRSVG_BUILD_DIR) && $(LINK) && mv $(RUST_LIB) .libs/librsvg_c_api.a
+       && cd $(LIBRSVG_BUILD_DIR) && $(LINK) $< && mv $(RUST_LIB) .libs/librsvg_c_api.a
 
 librsvg_@RSVG_API_MAJOR_VERSION@_la_CPPFLAGS = \
        -I$(top_srcdir)                         \
diff --git a/librsvg/dummy.c b/librsvg/dummy.c
new file mode 100644
index 00000000..061a78c3
--- /dev/null
+++ b/librsvg/dummy.c
@@ -0,0 +1,30 @@
+/* A dummy file, to prevent empty libraries from breaking builds.
+
+   This file is in the public domain.  -- Bruno Haible */
+
+/* Some systems, reportedly OpenBSD and Mac OS X, refuse to create
+   libraries without any object files.  You might get an error like:
+
+   > ar cru .libs/libgl.a
+   > ar: no archive members specified
+
+   Compiling this file, and adding its object file to the library, will
+   prevent the library from being empty.  */
+
+/* Some systems, such as Solaris with cc 5.0, refuse to work with libraries
+   that don't export any symbol.  You might get an error like:
+
+   > cc ... libgnu.a
+   > ild: (bad file) garbled symbol table in archive ../gllib/libgnu.a
+
+   Compiling this file, and adding its object file to the library, will
+   prevent the library from exporting no symbols.  */
+
+#ifdef __sun
+/* This declaration ensures that the library will export at least 1 symbol.  */
+int gl_dummy_symbol;
+#else
+/* This declaration is solely to ensure that after preprocessing
+   this file is never empty.  */
+typedef int dummy;
+#endif