PR26458 UBSAN: elf32-i386.c:3615 left shift of negative value

Happens when poking symbol index -2 into r_info.  (The index is
updated before writing out to file.)

	PR 26458
	* elf/common.h (ELF32_R_INFO): Cast symbol index to unsigned.

include/ChangeLog

@@ -1,3 +1,8 @@
+2020-08-26  Alan Modra  <amodra@gmail.com>
+
+	PR 26458
+	* elf/common.h (ELF32_R_INFO): Cast symbol index to unsigned.
+
 2020-08-24  Cooper Qu  <cooper.qu@linux.alibaba.com>
 
 	* opcode/csky.h (CSKYV2_ISA_10E60): New.

include/elf/common.h

@@ -942,7 +942,7 @@
 
 #define ELF32_R_SYM(i)		((i) >> 8)
 #define ELF32_R_TYPE(i)		((i) & 0xff)
-#define ELF32_R_INFO(s,t)	(((s) << 8) + ((t) & 0xff))
+#define ELF32_R_INFO(s,t)	(((unsigned) (s) << 8) + ((t) & 0xff))
 
 #define ELF64_R_SYM(i)		((i) >> 32)
 #define ELF64_R_TYPE(i)		((i) & 0xffffffff)