merge(third_party/git): Merge squashed git subtree at v2.23.0

Merge commit '1b593e1ea4' as 'third_party/git'

third_party/git/varint.c

@@ -0,0 +1,30 @@
+#include "git-compat-util.h"
+#include "varint.h"
+
+uintmax_t decode_varint(const unsigned char **bufp)
+{
+	const unsigned char *buf = *bufp;
+	unsigned char c = *buf++;
+	uintmax_t val = c & 127;
+	while (c & 128) {
+		val += 1;
+		if (!val || MSB(val, 7))
+			return 0; /* overflow */
+		c = *buf++;
+		val = (val << 7) + (c & 127);
+	}
+	*bufp = buf;
+	return val;
+}
+
+int encode_varint(uintmax_t value, unsigned char *buf)
+{
+	unsigned char varint[16];
+	unsigned pos = sizeof(varint) - 1;
+	varint[pos] = value & 127;
+	while (value >>= 7)
+		varint[--pos] = 128 | (--value & 127);
+	if (buf)
+		memcpy(buf, varint + pos, sizeof(varint) - pos);
+	return sizeof(varint) - pos;
+}