microblaze: lib: Add lib function declarations

Function declarations fix these sparse warnings:
arch/microblaze/lib/ashldi3.c:5:11: warning: symbol
	'__ashldi3' was not declared. Should it be static?
arch/microblaze/lib/muldi3.c:50:8: warning: symbol
	'__muldi3' was not declared. Should it be static?
arch/microblaze/lib/cmpdi2.c:5:11: warning: symbol
	'__cmpdi2' was not declared. Should it be static?
arch/microblaze/lib/lshrdi3.c:5:11: warning: symbol
	'__lshrdi3' was not declared. Should it be static?
arch/microblaze/lib/ashrdi3.c:5:11: warning: symbol
	'__ashrdi3' was not declared. Should it be static?
arch/microblaze/lib/ucmpdi2.c:5:11: warning: symbol
	'__ucmpdi2' was not declared. Should it be static?

Signed-off-by: Michal Simek <michal.simek@xilinx.com>

arch/microblaze/lib/libgcc.h

@@ -22,4 +22,11 @@ typedef union {
 	long long ll;
 } DWunion;
 
+extern long long __ashldi3(long long u, word_type b);
+extern long long __ashrdi3(long long u, word_type b);
+extern word_type __cmpdi2(long long a, long long b);
+extern long long __lshrdi3(long long u, word_type b);
+extern long long __muldi3(long long u, long long v);
+extern word_type __ucmpdi2(unsigned long long a, unsigned long long b);
+
 #endif /* __ASM_LIBGCC_H */