build: Add -Wshadow

samu.c: In function ‘main’:
samu.c:187:21: warning: declaration of ‘n’ shadows a previous local [-Wshadow]
  187 |                 int n = sysconf(_SC_NPROCESSORS_ONLN);
      |                     ^
samu.c:126:22: note: shadowed declaration is here
  126 |         struct node *n;
      |                      ^

Makefile

@@ -4,7 +4,7 @@
 PREFIX=/usr/local
 BINDIR=$(PREFIX)/bin
 MANDIR=$(PREFIX)/share/man
-ALL_CFLAGS=$(CFLAGS) -std=c99 -Wall -Wextra -Wpedantic -Wno-unused-parameter
+ALL_CFLAGS=$(CFLAGS) -std=c99 -Wall -Wextra -Wshadow -Wpedantic -Wno-unused-parameter
 OBJ=\
 	build.o\
 	deps.o\

samu.c

@@ -203,16 +203,16 @@ main(int argc, char *argv[])
 argdone:
 	if (!buildopts.maxjobs) {
 #ifdef _SC_NPROCESSORS_ONLN
-		int n = sysconf(_SC_NPROCESSORS_ONLN);
-		switch (n) {
+		int nproc = sysconf(_SC_NPROCESSORS_ONLN);
+		switch (nproc) {
 		case -1: case 0: case 1:
 			buildopts.maxjobs = 2;
 			break;
 		case 2:
 			buildopts.maxjobs = 3;
 			break;
 		default:
-			buildopts.maxjobs = n + 2;
+			buildopts.maxjobs = nproc + 2;
 			break;
 		}
 #else