Tweaks for Linux.

src/cmd/dc.c

diff --git a/src/cmd/dc.c b/src/cmd/dc.c
index 9fe4560..21967de 100644
--- a/src/cmd/dc.c
+++ b/src/cmd/dc.c
@@ -149,6 +149,7 @@
 int	command(void);
 int	cond(char c);
 void	load(void);
+#define log2 dclog2
 int	log2(long n);
 Blk*	salloc(int size);
 Blk*	morehd(void);

src/cmd/tail.c

diff --git a/src/cmd/tail.c b/src/cmd/tail.c
index 448b3ea..73e2b2d 100644
--- a/src/cmd/tail.c
+++ b/src/cmd/tail.c
@@ -39,6 +39,7 @@
 extern	void	skip(void);
 extern	void	suffix(char*);
 extern	long	tread(char*, long);
+#define trunc tailtrunc
 extern	void	trunc(Dir*, Dir**);
 extern	long	tseek(long, int);
 extern	void	twrite(char*, long);