Sync memmem.c and strstr.c with upstream musl

This diff merges two fixes from upstream musl. The first fixes a shift
overflow, the second fixes a comment. See:

https://git.musl-libc.org/cgit/musl/commit?id=593caa456309714402ca4cb77c3770f4c24da9da
https://git.musl-libc.org/cgit/musl/commit?id=c53e9b239418eb3e0e8be256abd0f6ad7608bbcf

OK?

Index: memmem.c
===================================================================
RCS file: /cvs/src/lib/libc/string/memmem.c,v
diff -p -u -r1.5 memmem.c
--- memmem.c	16 Apr 2020 12:39:28 -0000	1.5
+++ memmem.c	23 Jun 2026 12:11:21 -0000
@@ -38,8 +38,8 @@ twobyte_memmem(const unsigned char *h, s
 static char *
 threebyte_memmem(const unsigned char *h, size_t k, const unsigned char *n)
 {
-	uint32_t nw = n[0]<<24 | n[1]<<16 | n[2]<<8;
-	uint32_t hw = h[0]<<24 | h[1]<<16 | h[2]<<8;
+	uint32_t nw = (uint32_t)n[0]<<24 | n[1]<<16 | n[2]<<8;
+	uint32_t hw = (uint32_t)h[0]<<24 | h[1]<<16 | h[2]<<8;
 	for (h+=3, k-=3; k; k--, hw = (hw|*h++)<<8)
 		if (hw == nw) return (char *)h-3;
 	return hw == nw ? (char *)h-3 : 0;
@@ -48,8 +48,8 @@ threebyte_memmem(const unsigned char *h,
 static char *
 fourbyte_memmem(const unsigned char *h, size_t k, const unsigned char *n)
 {
-	uint32_t nw = n[0]<<24 | n[1]<<16 | n[2]<<8 | n[3];
-	uint32_t hw = h[0]<<24 | h[1]<<16 | h[2]<<8 | h[3];
+	uint32_t nw = (uint32_t)n[0]<<24 | n[1]<<16 | n[2]<<8 | n[3];
+	uint32_t hw = (uint32_t)h[0]<<24 | h[1]<<16 | h[2]<<8 | h[3];
 	for (h+=4, k-=4; k; k--, hw = hw<<8 | *h++)
 		if (hw == nw) return (char *)h-4;
 	return hw == nw ? (char *)h-4 : 0;
Index: strstr.c
===================================================================
RCS file: /cvs/src/lib/libc/string/strstr.c,v
diff -p -u -r1.9 strstr.c
--- strstr.c	16 Apr 2020 12:37:52 -0000	1.9
+++ strstr.c	23 Jun 2026 12:11:21 -0000
@@ -37,8 +37,8 @@ twobyte_strstr(const unsigned char *h, c
 static char *
 threebyte_strstr(const unsigned char *h, const unsigned char *n)
 {
-	uint32_t nw = n[0]<<24 | n[1]<<16 | n[2]<<8;
-	uint32_t hw = h[0]<<24 | h[1]<<16 | h[2]<<8;
+	uint32_t nw = (uint32_t)n[0]<<24 | n[1]<<16 | n[2]<<8;
+	uint32_t hw = (uint32_t)h[0]<<24 | h[1]<<16 | h[2]<<8;
 	for (h+=2; *h && hw != nw; hw = (hw|*++h)<<8);
 	return *h ? (char *)h-2 : 0;
 }
@@ -46,8 +46,8 @@ threebyte_strstr(const unsigned char *h,
 static char *
 fourbyte_strstr(const unsigned char *h, const unsigned char *n)
 {
-	uint32_t nw = n[0]<<24 | n[1]<<16 | n[2]<<8 | n[3];
-	uint32_t hw = h[0]<<24 | h[1]<<16 | h[2]<<8 | h[3];
+	uint32_t nw = (uint32_t)n[0]<<24 | n[1]<<16 | n[2]<<8 | n[3];
+	uint32_t hw = (uint32_t)h[0]<<24 | h[1]<<16 | h[2]<<8 | h[3];
 	for (h+=3; *h && hw != nw; hw = hw<<8 | *++h);
 	return *h ? (char *)h-3 : 0;
 }
@@ -129,7 +129,7 @@ twoway_strstr(const unsigned char *h, co
 	for (;;) {
 		/* Update incremental end-of-haystack pointer */
 		if (z-h < l) {
-			/* Fast estimate for MIN(l,63) */
+			/* Fast estimate for MAX(l,63) */
 			size_t grow = l | 63;
 			const unsigned char *z2 = memchr(z, 0, grow);
 			if (z2) {