Fix cross-compilation with mingw/linux (#758)

src/CMakeLists.txt

diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index e0f2ace..9ec3ca6 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -33,7 +33,7 @@
 
 # We need extra libraries on Windows
 if(${CMAKE_SYSTEM_NAME} MATCHES "Windows")
-  target_link_libraries(benchmark Shlwapi)
+  target_link_libraries(benchmark shlwapi)
 endif()
 
 set(include_install_dir "include")

src/colorprint.cc

diff --git a/src/colorprint.cc b/src/colorprint.cc
index 2dec4a8..fff6a98 100644
--- a/src/colorprint.cc
+++ b/src/colorprint.cc
@@ -25,7 +25,7 @@
 #include "internal_macros.h"
 
 #ifdef BENCHMARK_OS_WINDOWS
-#include <Windows.h>
+#include <windows.h>
 #include <io.h>
 #else
 #include <unistd.h>

src/sleep.cc

diff --git a/src/sleep.cc b/src/sleep.cc
index 54aa04a..1512ac9 100644
--- a/src/sleep.cc
+++ b/src/sleep.cc
@@ -21,7 +21,7 @@
 #include "internal_macros.h"
 
 #ifdef BENCHMARK_OS_WINDOWS
-#include <Windows.h>
+#include <windows.h>
 #endif
 
 namespace benchmark {

src/sysinfo.cc

diff --git a/src/sysinfo.cc b/src/sysinfo.cc
index 90be166..7b2285b 100644
--- a/src/sysinfo.cc
+++ b/src/sysinfo.cc
@@ -15,9 +15,9 @@
 #include "internal_macros.h"
 
 #ifdef BENCHMARK_OS_WINDOWS
-#include <Shlwapi.h>
-#include <VersionHelpers.h>
-#include <Windows.h>
+#include <shlwapi.h>
+#include <versionhelpers.h>
+#include <windows.h>
 #else
 #include <fcntl.h>
 #include <sys/resource.h>

src/timers.cc

diff --git a/src/timers.cc b/src/timers.cc
index 817272d..30743c5 100644
--- a/src/timers.cc
+++ b/src/timers.cc
@@ -16,9 +16,9 @@
 #include "internal_macros.h"
 
 #ifdef BENCHMARK_OS_WINDOWS
-#include <Shlwapi.h>
-#include <VersionHelpers.h>
-#include <Windows.h>
+#include <shlwapi.h>
+#include <versionhelpers.h>
+#include <windows.h>
 #else
 #include <fcntl.h>
 #include <sys/resource.h>