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

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

third_party/git/compat/setenv.c

@@ -0,0 +1,40 @@
+#include "../git-compat-util.h"
+
+int gitsetenv(const char *name, const char *value, int replace)
+{
+	int out;
+	size_t namelen, valuelen;
+	char *envstr;
+
+	if (!name || strchr(name, '=') || !value) {
+		errno = EINVAL;
+		return -1;
+	}
+	if (!replace) {
+		char *oldval = NULL;
+		oldval = getenv(name);
+		if (oldval) return 0;
+	}
+
+	namelen = strlen(name);
+	valuelen = strlen(value);
+	envstr = malloc(st_add3(namelen, valuelen, 2));
+	if (!envstr) {
+		errno = ENOMEM;
+		return -1;
+	}
+
+	memcpy(envstr, name, namelen);
+	envstr[namelen] = '=';
+	memcpy(envstr + namelen + 1, value, valuelen);
+	envstr[namelen + valuelen + 1] = 0;
+
+	out = putenv(envstr);
+	/* putenv(3) makes the argument string part of the environment,
+	 * and changing that string modifies the environment --- which
+	 * means we do not own that storage anymore.  Do not free
+	 * envstr.
+	 */
+
+	return out;
+}