Add missing library header guards (#181)

## Description

All header files should include header guards.

Some header files, such as those which define structures,
cannot be included more than once within a translation unit, as doing
so would cause a redefinition error. Such headers must be guarded to
prevent ill-effects from multiple inclusion. Similarly, if header
files include other header files, and this inclusion graph contains
a cycle, then at least one file within the cycle must contain header
guards in order to break the cycle. Because of cases like these, all
headers should be guarded as a matter of good practice, even if they
do not strictly need to be.

Furthermore, most modern compilers contain optimizations which are
triggered by header guards. If the header guard strictly conforms
to the pattern that compilers expect, then inclusions of that
header other than the first have absolutely no effect: the file
isn't re-read from disk, nor is it re-tokenised or re-preprocessed.
This can result in a noticeable, albeit minor, improvement to
compilation time.

- [ ] Impacts functionality?
- **Functionality** - Does the change ultimately impact how firmware
functions?
- Examples: Add a new library, publish a new PPI, update an algorithm,
...
- [ ] Impacts security?
- **Security** - Does the change have a direct security impact on an
application,
    flow, or firmware?
  - Examples: Crypto algorithm change, buffer overflow fix, parameter
    validation improvement, ...
- [ ] Breaking change?
- **Breaking change** - Will anyone consuming this change experience a
break
    in build or boot behavior?
- Examples: Add a new library class, move a module to a different repo,
call
    a function in a new library class in a pre-existing module, ...
- [ ] Includes tests?
  - **Tests** - Does the change include any explicit test code?
  - Examples: Unit tests, integration tests, robot tests, ...
- [ ] Includes documentation?
- **Documentation** - Does the change contain explicit documentation
additions
    outside direct code modifications (and comments)?
- Examples: Update readme file, add feature readme file, link to
documentation
    on an a separate Web page, ...

## How This Was Tested

- Compilation
- CodeQL

## Integration Instructions

N/A

Signed-off-by: Michael Kubacki <[email protected]>

DfciPkg/Include/Library/DfciAssetTagSettingLib.h

@@ -8,6 +8,9 @@ SPDX-License-Identifier: BSD-2-Clause-Patent
 
 **/
 
+#ifndef DFCI_ASSET_TAG_SETTING_LIB_H_
+#define DFCI_ASSET_TAG_SETTING_LIB_H_
+
 /**
  * Settings Provider AssetTagGet routine for pre SettingsManager access.
  *
@@ -25,3 +28,5 @@ DfciGetAssetTag (
   IN  OUT   UINTN  *ValueSize,
   OUT       VOID   *Value
   );
+
+#endif

DfciPkg/Include/Library/DfciGroupLib.h

@@ -8,6 +8,9 @@ SPDX-License-Identifier: BSD-2-Clause-Patent
 
 **/
 
+#ifndef DFCI_GROUP_LIB_H_
+#define DFCI_GROUP_LIB_H_
+
 typedef struct {
   DFCI_SETTING_ID_STRING    GroupId;               // Pointer to Group Id
   DFCI_SETTING_ID_STRING    *GroupMembers;         // Pointer to array of Setting Id's
@@ -26,3 +29,5 @@ EFIAPI
 DfciGetGroupEntries (
   VOID
   );
+
+#endif

DfciPkg/Include/Library/DfciSettingChangedNotificationLib.h

@@ -8,6 +8,9 @@ SPDX-License-Identifier: BSD-2-Clause-Patent
 
 **/
 
+#ifndef DFCI_SETTING_CHANGED_NOTIFICATION_LIB_H_
+#define DFCI_SETTING_CHANGED_NOTIFICATION_LIB_H_
+
 /**
  * Process Setting Changed    - Called for any setting that has changed.  Not called when a setting
  *                              has not changed.  The setting value is also supplied.
@@ -48,3 +51,5 @@ EFIAPI
 DfciSettingChangedResetNotification (
   VOID
   );
+
+#endif

DfciPkg/Include/Library/DfciV1SupportLib.h

@@ -8,6 +8,9 @@ SPDX-License-Identifier: BSD-2-Clause-Patent
 
 **/
 
+#ifndef DFCI_V1_SUPPORT_LIB_H_
+#define DFCI_V1_SUPPORT_LIB_H_
+
 /**
  * Return V2 string from V1 Id String
  *
@@ -49,3 +52,5 @@ EFIAPI
 DfciV1NumberFromId (
   DFCI_SETTING_ID_STRING  Id
   );
+
+#endif