Specify output explicitly for the .c.o compile rule

newlib/libc/sys/nacl/Makefile.am

Index: newlib/libc/sys/nacl/Makefile.am
diff --git a/newlib/libc/sys/nacl/Makefile.am b/newlib/libc/sys/nacl/Makefile.am
index a5463bc0cb81212b5b18ab3593c997b531ac2a0d..c64be1ba0556b11a7ff4767f22505147d7547e10 100644
--- a/newlib/libc/sys/nacl/Makefile.am
+++ b/newlib/libc/sys/nacl/Makefile.am
@@ -12,6 +12,15 @@ lib_a_SOURCES = dummysys.c aeabi_atexit.c
 lib_a_CCASFLAGS = $(AM_CCASFLAGS)
 lib_a_CFLAGS = $(AM_CFLAGS)
 
+## The automatically generated .c.o rule in Makefile.in does not specify the
+## output file name even though upper level Makefile assumes that the output
+## filename is crt0.o. However, this breaks when the compiler does not use .o
+## extension for object files. Newer Automake already specifies the output
+## filename, but since Newlib does not currently build with newer
+## Autoconf/Automake versions, we need to override the rule manually.
+.c.o:
+	$(COMPILE) -c $< -o $@
+
 all: crt0.o
 
 ACLOCAL_AMFLAGS = -I ../../.. -I ../../../..