Implement minimalistic strcasestr (#5411)

* Implement minimalistic strcasestr

* fixup! Implement minimalistic strcasestr

* Add _GNU_SOURCE

Enable gcc extensions

* fixup! fixup! Implement minimalistic strcasestr

Makefile

@@ -206,6 +206,7 @@ CFLAGS     += $(ARCH_FLAGS) \
               -fdata-sections \
               -pedantic \
               $(DEVICE_FLAGS) \
+              -D_GNU_SOURCE \
               -DUSE_STDPERIPH_DRIVER \
               -D$(TARGET) \
               $(TARGET_FLAGS) \

src/main/common/string_light.c

@@ -78,3 +78,15 @@ int strncasecmp(const char * s1, const char * s2, size_t n)
 
     return d;
 }
+
+char *strcasestr(const char *haystack, const char *needle)
+{
+    int nLen = strlen(needle);
+    do {
+        if (!strncasecmp(haystack, needle, nLen)) {
+            return (char *)haystack;
+        }
+        haystack++;
+    } while (*haystack);
+    return NULL;
+}