This makes _alpm_filelist_difference() and _alpm_filelist_intersection() take
into account that filenames are case insensitive (only for ASCII, unicode is
still broken). This fixes conflict detection in case two packages share the
same filename with a different case.
--- pacman-5.1.1-orig/lib/libalpm/filelist.c	2018-05-14 02:02:18.000000000 +0200
+++ pacman-5.1.1/lib/libalpm/filelist.c	2018-09-28 13:05:47.398469000 +0200
@@ -25,6 +25,43 @@
 #include "filelist.h"
 #include "util.h"
 
+#ifdef __MSYS__
+
+#define TOLOWER(c) (((c) >= 'A' && (c) <= 'Z') ? (c) - 'A' + 'a' : (c))
+
+static int _cmppath(const char *s1, const char *s2)
+{
+	int c1, c2;
+
+	while(*s1 && *s2)
+	{
+		c1 = TOLOWER(*s1);
+		c2 = TOLOWER(*s2);
+		if(c1 != c2)
+			return c1 - c2;
+		s1++;
+		s2++;
+	}
+
+	return *s1 - *s2;
+}
+
+static int _cmpchar(char c1, char c2)
+{
+	return TOLOWER(c1) - TOLOWER(c2);
+}
+#else
+static int _cmppath(const char *s1, const char *s2)
+{
+	return strcmp(s1, s2);
+}
+
+static int _cmpchar(char c1, char c2)
+{
+	return c1 - c2;
+}
+#endif
+
 /* Returns the difference of the provided two lists of files.
  * Pre-condition: both lists are sorted!
  * When done, free the list but NOT the contained data.
@@ -39,7 +76,7 @@
 		char *strA = filesA->files[ctrA].name;
 		char *strB = filesB->files[ctrB].name;
 
-		int cmp = strcmp(strA, strB);
+		int cmp = _cmppath(strA, strB);
 		if(cmp < 0) {
 			/* item only in filesA, qualifies as a difference */
 			ret = alpm_list_add(ret, strA);
@@ -63,7 +100,7 @@
 
 static int _alpm_filelist_pathcmp(const char *p1, const char *p2)
 {
-	while(*p1 && *p1 == *p2) {
+	while(*p1 && _cmpchar(*p1, *p2) == 0) {
 		p1++;
 		p2++;
 	}
@@ -75,7 +112,7 @@
 		p1++;
 	}
 
-	return *p1 - *p2;
+	return _cmpchar(*p1, *p2);
 }
 
 /* Returns the intersection of the provided two lists of files.
@@ -115,7 +152,7 @@
 {
 	const alpm_file_t *file1 = f1;
 	const alpm_file_t *file2 = f2;
-	return strcmp(file1->name, file2->name);
+	return _cmppath(file1->name, file2->name);
 }
 
 alpm_file_t SYMEXPORT *alpm_filelist_contains(alpm_filelist_t *filelist,
@@ -137,7 +174,7 @@
 {
 	size_t i;
 	for(i = 1; i < filelist->count; i++) {
-		if(strcmp(filelist->files[i - 1].name, filelist->files[i].name) > 0) {
+		if(_cmppath(filelist->files[i - 1].name, filelist->files[i].name) > 0) {
 			/* filelist is not pre-sorted */
 			qsort(filelist->files, filelist->count,
 					sizeof(alpm_file_t), _alpm_files_cmp);