Fix build on platforms where __USER_LABEL_PREFIX__ is not empty

On most platforms, a C language symbol and its assembly equivalent are
identical. However, on the Blackfin architecture, this isn't the case,
the corresponding C language symbol in assembly is prepended with a
"_". Blackfin therefore has __USER_LABEL_PREFIX__ defined to "_".

Cairo already has some code to cope with __USER_LABEL_PREFIX__, but
this code isn't completely correct: it prepends both assembly symbols
and C symbols with __USER_LABEL_PREFIX__, which cannot work.

This patch fixes that by using the existing slim_hidden_asmname() to
define assembly symbols, and introduce a new slim_hidden_realname()
for C symbols.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

Index: b/src/cairo-compiler-private.h
===================================================================
--- a/src/cairo-compiler-private.h
+++ b/src/cairo-compiler-private.h
@@ -93,12 +93,13 @@
 	__asm__ (slim_hidden_asmname (internal))
 # define slim_hidden_def1(name, internal)				\
   extern __typeof (name) EXT_##name __asm__(slim_hidden_asmname(name))	\
-	__attribute__((__alias__(slim_hidden_asmname(internal))))
+	__attribute__((__alias__(slim_hidden_realname(internal))))
 # define slim_hidden_ulp		slim_hidden_ulp1(__USER_LABEL_PREFIX__)
 # define slim_hidden_ulp1(x)		slim_hidden_ulp2(x)
 # define slim_hidden_ulp2(x)		#x
 # define slim_hidden_asmname(name)	slim_hidden_asmname1(name)
 # define slim_hidden_asmname1(name)	slim_hidden_ulp #name
+# define slim_hidden_realname(name)     #name
 #else
 # define slim_hidden_proto(name)		int _cairo_dummy_prototype(void)
 # define slim_hidden_proto_no_warn(name)	int _cairo_dummy_prototype(void)
